A quantitative analysis of activation process during hold time under creep-fatigue interaction conditions has been interpreted for 1Cr-Mo-V steel. The apparent activation energy for stress relaxation at the saturated stage was the same for the lattice diffusion activation energy of iron i.e. 251 kJ mol(-1) independent of the total strain range. Analyzing the value of the activation volume for the initial transient relaxation behavior, it is suggested that the rate controlling dislocation mechanism is either cross slip, or overcoming Peierls-Nabarro stress. The trend of increasing activation energy with the relaxed stress was found to be due to the effective stress which was decreased with time and approached to zero. (C) 1999 Elsevier Science S.A. All rights reserved.