Was the Mii created on the Wii console you are trying to edit it on? Miis imported from other Wii consoles cannot be edited.

Are you selecting "Save and Quit" when finished editing? If not, no edits will be saved.

Go to the Mii Channel and create a new Mii (click here here for instructions for creating a Mii for the first time or click here for creating a new Mii).

1. Once the Mii is created, verify that it shows up in the Mii Plaza.
2. Power off the console, then power it back on and go back to the Mii Channel.
3. If the Mii is still there, the console is able to save fine.
4. If the Mii is not there, press the whistle icon to arrange your Miis to verify that it hasn't simply wandered off the screen.