Abstract The aim of this paper is to present results of creep experiments carried out on thin-walled tubular specimens of pure copper under combined tension and torsion at 573 K. The experimental program consists of creep tests for the material in the virgin state, and for the same material prestrained plastically at the room temperature by uniaxial tension or by pure torsion. The modified Norton's law, based on experimental observations, was proposed to describe the rate of secondary creep. This modification is based on the assumption that the material parameters may be expressed as the functions depending on the direction of the loading stress vector. Results are discussed in terms of a creep surface concept. The changes in size and shape of the creep surfaces caused by plastic prestrains express the evolution of the initial creep surface for virgin material.