In this study, finite element buckling analyses of transversely stiffened isotropic and orthotropic rectangular thin plates under shear loads are presented. Eigenvalue buckling analysis is used to predict critical buckling loads of mild steel and Boron-Aluminium MMC composite stiffened plates with different fiber orientations by using ANSYS. A simply supported boundary condition is applied through the edges of the plates and uniformly distributed shear loads are given to edge nodes. It is demonstrated that by adding more transverse rectangular stiffeners which are made of the same material with the plate, critical buckling stress of the plates increases linearly. The failure tests of unstiffened Boron-Aluminium plates were performed according to Tsai-Hill failure criteria.