The present study is concerned with the elastic/plastic buckling of a thin rectangular plate when nonlinear strain terms are put into consideration in the equation of uniqueness. Buckling analyses of the plate was placed under different loading conditions i.e. uniaxial compression, biaxial compression and pure shear loading. The equilibrium and stability equations are derived and analysed based on the elastic theory presented by Hooke’s law and two theories of plasticity i.e. deformation theory (DT) and incremental theory (IT). Rayleigh-Ritz method was used as a discretization technique to solve the buckling of plate equation. A comparison of results between nonlinear strains versus linear strains was carried out and a 6.7% difference was observed when the plate was subjected to pure shear loading. The variation between the two cases was seen to increase as boundary equations became complicated when pure shear stress was considered. Furthermore, different parameters have been discussed i.e., effects of aspect ratio, thickness to width ratio and loading ratios, effect of different boundary condition and the type of plasticity theory considered.