  We have discussed non-linear stability in photogravitational non-planar
restricted three body problem with oblate smaller primary. By
photogravitational we mean that both primaries are radiating. We normalised the
Hamiltonian using Lie transform as in Coppola and Rand (1989). We transformed
the system into Birkhoff's normal form. Lie transforms reduce the system to an
equivalent simpler system which is immediately solvable. Applying Arnold's
theorem, we have found non-linear stability criteria. We conclude that $L_6$ is
stable. We plotted graphs for $(\omega_1, D_2).$ They are rectangular
hyperbola.
