Three-dimensional buckling analysis of rectangular plates has been carried out by using Ritz method. The three displacement components of the plates are expanded in three directions by the series of Chebyshev polynomial multiplied by the boundary function which makes the expansions satisfy the essential boundary conditions along the edges. The eigenvalue matrix for buckling loads is obtained for rectangular plates. The comparisons of the results of simply supported and clamped plates with different thickness-side and aspect ratios with the published results show good agreements. Finally, the three-dimensional buckling modes are plotted. © 2010 American Institute of Physics.