On the basis of yon Karman equations and using the general bifurcation theory, the elastic instability of an orthotropic elliptic plate whose edge is subjected to a uniform plane compression is discussed. Following the well-known Liapunov-Schmidt process the existance of bifurcation solution at a simple eigenvalue is shown and the asymptotic expression is obtained by means of the perturbation expansion with a small parameter. Finally, by using the finite element method, the critical loads of the plate are computed and the post-buckling behavior is analysed. And also the effect of material and geome-tric parameters on the stability is studied.