She made an appearance Wednesday in Philadelphia, where the U.S. Conference of Mayors is having its annual leadership meeting.
The first lady says solving the childhood obesity problem is not a political issue, but about the future of our children. And she says everyone has to work together to solve it.
Mrs. Obama is urging more communities to join in her two-year-old "Let's Move!" effort to combat obesity and improve healthy eating and fitness, especially for young people.
"Many of the best solutions start in our city halls or our towns or county councils - they start with leaders like the men and women on stage who see peoples' struggles up close," said the first lady.
There's a new website where elected officials can sign a pledge to get involved. In exchange they get tips on how to raise funds for their own programs and how to enhance the ones they already have.
Appearing with the first lady were about a dozen mayors of other cities that have established programs to encourage healthy eating and exercise.
Kids at the event today also got to play with a new KaBoom playground. And many are taking the first lady's visit and her message to heart," said Jeremy Jackson.
"I think if you live healthy, then I think you live longer, you have to stay fit and can't be in your house all day," said one.
Najee Melton said his plan was to, "Exercise, eat vegetables and jog with my dad."