The basic equations are proposed for plastic deformation of porous metals such as sintered metal powders or metal powder compacts. The porous metal is assumed to be made up of a homogeneous metallic material and unformly distributed pores. The following equations are obtained from the Levy-Mises equatioins, (dε₁-dε₂)/(σ₁-σ₂)=(dε₂-dε₃)/(σ₂-σ₃)=(dε₃-dε₁)/(σ₃-σ₁)=(3fdε_υ)/(2σ_m/f)=(3dε_eq)/(2γσ_eq) where γ is the relative density of the porous metal, f a function of γ, the subscripts 1, 2 and 3 represent the principal directions, σ_m=(σ₁+σ₂+σ₃)/3 and dε_υ=dε₁+dε₂+dε₃. The theory shows a good agreement with the experimental results for sintered copper powder compacts.