We have discussed the nonlinear stability of triangular equilibrium points in generalized photogravitational restricted three body problem. The problem is generalized in the sense that both primaries are taken as oblate spheroid. We have performed first and second normalization of the Hamiltonian of the problem We have applied Arnold’s theorem to examine the condition of non-linear stability. We have found three critical mass ratios where this theorem fails. The stability condition is different from the classical case due to radiation and oblateness of the primaries.