What About Mimi is a snappy, savvy, family-oriented show about 11-year-old Mimi Morton: problem-solver extraordinaire! Mimi trains her earnest problem-fixing skills on her friends and family, to hilarious and varying results!

Mimi Mortin (voiced by Chiara Zanni) - A clever, optimistic, red-headed, 11-year old girl in the sixth grade who is an excellent problem-solver, and is able to solve any trouble with a little help from her friends (and sometimes her rivals and enemies) and with the power of her imagination.

Elaine Petuskin (voiced by Kori Cook) - Mimi's friend who is of Asian descent (presumably Japanese or Chinese). She is an animal lover, and owns lots of pets.

Russell Van Eden (voiced by Rhys Huber) - A sidekick of Mimi's who apparently has a crush on Sincerity.

Sincerity Travers (voiced by Carly McKillip) - A snobbish preppy teenybopper with pink hair who, sometimes, does not get along with Mimi. She and Mimi used to be friends years ago, but as they got older, their interests diverged, and they started growing apart. She is Mimi's rival in school, and although she does not get along with her, she admits that her ideas are pretty good and helps with some of her schemes. Even if she does not get along with Mimi, she has a resentful respect for her, showing that deep inside, Sincerity still considers her as a true friend.

Brock Wickersham (voiced by Tony Sampson) - A big bully who enjoys pulling pranks on various characters.

Budweiser "Buddy" Wickersham (voiced by Andrew Francis) - Brock's younger brother who is also a bully. It is also revealed that he is a genius, but he does not want people to find out about it, especially his big brother, saying that that fact would embarrass him in front of his family.

Brad "Bradley" Mortin (voiced by Keith William Miller) - Mimi's younger brother who knows that Mimi's plans always have flaws.

Jason Mortin (voiced by Samuel Vincent) - Mimi's older teenage brother who thinks of himself as an on-the-edge rebel.

Saffron Mortin (voiced by Pam Ferris) - Mimi's mother. She is a vegan, and always feeds her children vegetables.

Marvin "Marv" Mortin (voiced by Ray Ray F.R.) - Mimi's father.

Hayley Kitchensinker - One of Sincerity's lackeys, although she likes Mimi and Elaine and is kind.

Herbert Finkle - A nerd at Mimi's school who is of Russian descent.

Lodeman - A student at Mimi's school who tends to make rude noises all the time.

Ms. Victoria Frances Grindstone (voiced by Mindy Sterling) - Mimi's teacher.

Mr. Petri - A science teacher who blames Brock for everything bad (even over things Brock never did) because of his state of being a bully and for pulling multiple pranks inside of his classroom.

Mr. Jacques - A gym teacher.

Ms. Murchison - The librarian of Starfish Bay School. She and Mr. Pianoforte hate each other.

Principal Earl - The principal of Starfish Bay School.

Mr. Pianoforte - A musician. He and Ms. Murchison hate each other.