Abstract: Plastic deformation anisotropy of LC4 aluminum alloy （Al-Zn-Mg-Cu） plate is investigated. A method for expression and measurement of the plastic deformation anisotropy is proposed, by which different heat-treated uniaxial tensile specimens cut along the longitudinal direction of the plate have been tested, measured and analyzed. The conclusions are as follows: （1） The plastic strain in transverse direction （εT） and the plastic strain in the short transverse direction （εL） both increase linearly with the strain in longitudinal direction （εL）;（2） The plastic strain in short transverse direction is always larger than the plastic strain in transverse direction; （3） dεs/dεT is a proper parameter to express the plastic deformation anisotropy because it does not change with εL; （4） Different heat treatments have different effects on the anisotropy, and the anisotropy w akens with intensification of aging; （5） It seems that the sensitivity of shear failure is related with the plastic deformation anisotropy of the alloy.