Abstact The present study is concerned with the elastic/plastic buckling of thin rectangular plates when nonlinear strain terms are put into consideration instead of them being neglected from the equation of uniqueness. The in-plane loads are placed uniformly in the uniaxial compression, biaxial compression and pure shear loading. The equilibrium and stability equations are derived and analyses are carried out based on two theories of plasticity, i.e. deformation theory (DT) and incremental theory (IT). The elastic/plastic behavior of plates is described by the Ramberg–Osgood model. Rayleigh-Ritz method is used as a discretization technique to solve the buckling of plate equation. To examine accuracy of the present formulation and procedure, several convergence and comparison studies are investigated and new results are presented. Results obtained when nonlinear strain terms were used are compare with those when these terms are neglected. A 6.7% difference is observed when the plate was subject to pure shear loading and as boundary equations became complicated a larger variation is seen. The type of plasticity theory used determines the buckling mode to be achieved. Some unusual mode switching we observed in some cases when the aspect ratio was less than 1. Furthermore, effects of aspect, thickness to length and loading ratios, boundary condition, type of plasticity theory and linearly varying in-plane loading on the buckling coefficient are discussed. Key Words Incremental theory (IT), Deformation theory(DT), Nonlinear strains, Linear strains