Based on the double exponential behaviour of the gas mass profile and on the O/H gradient, Robles-Valdez, Carigi & Peimbert (2013) built a sucessful chemical evolution model for M33. The model predicts that in the inner parts of M33 the star formation history follows an inside-out scenario, like M31 or the MW, but in the outer parts of M33 the star formation history follows an outside-in scenario, as dwarf galaxies of the Local Group.