diff --git a/madb.go b/madb.go
index 8020832..b6560a1 100644
--- a/madb.go
+++ b/madb.go
@@ -362,6 +362,14 @@
 	UserIDs map[string]string
 }
 
+func newConfig() *config {
+	return &config{
+		Names:   make(map[string]string),
+		Groups:  make(map[string][]string),
+		UserIDs: make(map[string]string),
+	}
+}
+
 // Returns the config dir located at "~/.madb"
 func getConfigDir() (string, error) {
 	home := os.Getenv("HOME")
@@ -374,9 +382,68 @@
 		return "", err
 	}
 
+	if err := migrateOldConfigFiles(configDir); err != nil {
+		fmt.Fprintf(os.Stderr, "WARNING: Could not successfully migrate the old config files to the newer format: %v", err)
+	}
+
 	return configDir, nil
 }
 
+// migrateOldConfigFiles checks if there are old config files (for madb v1.x) in
+// the provided config directory. If there are, it migrates these configs to the
+// new format, so that users can preserve their device nicknames and user IDs
+// when upgrading madb to a newer version.
+// TODO(youngseokyoon): remove this migration code in the future.
+func migrateOldConfigFiles(configDir string) error {
+	// Do not try migrating if the new format "config" file already exists.
+	configFile := filepath.Join(configDir, "config")
+	if _, err := os.Stat(configFile); err == nil {
+		return nil
+	}
+
+	cfg := newConfig()
+	if err := migrateOldConfig(configDir, "nicknames", &cfg.Names); err != nil {
+		return err
+	}
+	if err := migrateOldConfig(configDir, "users", &cfg.UserIDs); err != nil {
+		return err
+	}
+	return writeConfig(cfg, configFile)
+}
+
+// migrateOldConfig reads an old config file, which contains a JSON-encoded map,
+// and writes the contents to the given map pointer (data).
+func migrateOldConfig(configDir, filename string, data *map[string]string) error {
+	configFile := filepath.Join(configDir, filename)
+	if _, err := os.Stat(configFile); os.IsNotExist(err) {
+		return nil
+	}
+
+	f, err := os.Open(configFile)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	decoder := json.NewDecoder(f)
+
+	if err := decoder.Decode(data); err != nil {
+		data = new(map[string]string)
+		return fmt.Errorf("Could not read the old config file %q: %v", filename, err)
+	}
+
+	fmt.Printf("NOTE: Migrating the %q file to the newer format.\n", filename)
+
+	// Rename the old config as a backup
+	if err := os.Rename(configFile, configFile+".bak"); err != nil {
+		return fmt.Errorf("Could not rename the %q file: %v", filename, err)
+	}
+
+	fmt.Printf("NOTE: The backup file can be found at %q.\n", filepath.Join(configDir, filename+".bak"))
+
+	return nil
+}
+
 // getDefaultConfigFilePath returns the default location of the config file.
 func getDefaultConfigFilePath() (string, error) {
 	configDir, err := getConfigDir()
@@ -391,13 +458,10 @@
 // When the file does not exist, it returns an empty config with the members
 // initialized as empty maps.
 func readConfig(filename string) (*config, error) {
-	result := new(config)
+	result := newConfig()
 
 	// The file may not exist or be empty when there are no stored data.
 	if stat, err := os.Stat(filename); os.IsNotExist(err) || (err == nil && stat.Size() == 0) {
-		result.Names = make(map[string]string)
-		result.Groups = make(map[string][]string)
-		result.UserIDs = make(map[string]string)
 		return result, nil
 	}
 
diff --git a/madb_test.go b/madb_test.go
index e9bf5f0..2444704 100644
--- a/madb_test.go
+++ b/madb_test.go
@@ -7,6 +7,7 @@
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -584,3 +585,120 @@
 		}
 	}
 }
+
+func TestConfigMigration(t *testing.T) {
+	tests := []struct {
+		configDir string
+		fileMap   map[string]string
+		want      config
+	}{
+		{
+			"testdata/configs/newFormat",
+			map[string]string{"config": "config"},
+			config{
+				Version: version,
+				Names:   map[string]string{"nickname01": "serial01", "nickname02": "serial02"},
+				Groups:  map[string][]string{},
+				UserIDs: map[string]string{"serial01": "10"},
+			},
+		},
+		{
+			"testdata/configs/oldFormatBoth",
+			map[string]string{"": "config", "nicknames": "nicknames.bak", "users": "users.bak"},
+			config{
+				Version: version,
+				Names:   map[string]string{"nickname01": "serial01", "nickname02": "serial02"},
+				Groups:  map[string][]string{},
+				UserIDs: map[string]string{"serial01": "10"},
+			},
+		},
+		{
+			"testdata/configs/oldFormatNicknamesOnly",
+			map[string]string{"": "config", "nicknames": "nicknames.bak"},
+			config{
+				Version: version,
+				Names:   map[string]string{"nickname01": "serial01", "nickname02": "serial02"},
+				Groups:  map[string][]string{},
+				UserIDs: map[string]string{},
+			},
+		},
+		{
+			"testdata/configs/oldFormatUsersOnly",
+			map[string]string{"": "config", "users": "users.bak"},
+			config{
+				Version: version,
+				Names:   map[string]string{},
+				Groups:  map[string][]string{},
+				UserIDs: map[string]string{"serial01": "10"},
+			},
+		},
+	}
+
+	for i, test := range tests {
+		// Copy the files in configDir to a temporary directory.
+		tempConfigDir, err := ioutil.TempDir("", "madbConfigTest")
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer os.RemoveAll(tempConfigDir)
+
+		files, err := ioutil.ReadDir(test.configDir)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		for _, file := range files {
+			src, err := os.Open(filepath.Join(test.configDir, file.Name()))
+			if err != nil {
+				t.Fatal(err)
+			}
+			dst, err := os.Create(filepath.Join(tempConfigDir, file.Name()))
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			_, err = io.Copy(dst, src)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			src.Close()
+			dst.Close()
+		}
+
+		// Run the migration.
+		migrateOldConfigFiles(tempConfigDir)
+
+		// Check the resulting config
+		cfg, err := readConfig(filepath.Join(tempConfigDir, "config"))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got, want := *cfg, test.want; !reflect.DeepEqual(got, want) {
+			t.Fatalf("unmatched results for tests[%v]: got %v, want %v", i, got, want)
+		}
+
+		// Check the file mapping.
+		for oldFile, newFile := range test.fileMap {
+			if oldFile == "" {
+				if _, err := os.Stat(filepath.Join(tempConfigDir, newFile)); os.IsNotExist(err) {
+					t.Fatalf("missing an expected config file %q", newFile)
+				}
+				continue
+			}
+
+			oldBytes, err := ioutil.ReadFile(filepath.Join(test.configDir, oldFile))
+			if err != nil {
+				t.Fatal(err)
+			}
+			newBytes, err := ioutil.ReadFile(filepath.Join(tempConfigDir, newFile))
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if bytes.Compare(oldBytes, newBytes) != 0 {
+				t.Fatalf("unmatched file contents between %q and %q.", oldFile, newFile)
+			}
+		}
+	}
+}
diff --git a/testdata/configs/newFormat/config b/testdata/configs/newFormat/config
new file mode 100644
index 0000000..0776102
--- /dev/null
+++ b/testdata/configs/newFormat/config
@@ -0,0 +1 @@
+{"Version":"v1.1.1-develop","Names":{"nickname01":"serial01","nickname02":"serial02"},"Groups":{},"UserIDs":{"serial01":"10"}}
diff --git a/testdata/configs/oldFormatBoth/nicknames b/testdata/configs/oldFormatBoth/nicknames
new file mode 100644
index 0000000..99b1adb
--- /dev/null
+++ b/testdata/configs/oldFormatBoth/nicknames
@@ -0,0 +1 @@
+{"nickname01":"serial01","nickname02":"serial02"}
diff --git a/testdata/configs/oldFormatBoth/users b/testdata/configs/oldFormatBoth/users
new file mode 100644
index 0000000..bbf7890
--- /dev/null
+++ b/testdata/configs/oldFormatBoth/users
@@ -0,0 +1 @@
+{"serial01":"10"}
diff --git a/testdata/configs/oldFormatNicknamesOnly/nicknames b/testdata/configs/oldFormatNicknamesOnly/nicknames
new file mode 100644
index 0000000..99b1adb
--- /dev/null
+++ b/testdata/configs/oldFormatNicknamesOnly/nicknames
@@ -0,0 +1 @@
+{"nickname01":"serial01","nickname02":"serial02"}
diff --git a/testdata/configs/oldFormatUsersOnly/users b/testdata/configs/oldFormatUsersOnly/users
new file mode 100644
index 0000000..bbf7890
--- /dev/null
+++ b/testdata/configs/oldFormatUsersOnly/users
@@ -0,0 +1 @@
+{"serial01":"10"}