Inteal stress and yield strength of pure copper films on substrates were characterized by x-ray diffraction and thermal-cycle substrate curvature methods. The inteal stress was of tension, and decreased with increasing workinggas (argon) pressure and increased with increasing film thickness. Tensile yield strength of copper films on steel substrate was reciprocal to the film thickness. Similarly, the compressive yield strength depended strongly on the film thickness:the thinner the film thickness, the larger the compressive yield strength.