I will present some results on the existence and nonlinear stability for the rotating star solutions which are axi-symmetric steady-state solutions of the compressible isentropic Euler-Poisson equations in 3 spatial dimensions. We then apply these results to rotating white dwarf stars to show its dynamical stability when the total mass is less than a critical mass, which is related to the "Chandrasekhar"limit in astrophysics. This is a joint work with Joel Smoller.