[en] A unified constitutive model incorporating dynamic strain aging effect was developed in order to describe inelastic behavior of Mod. 9Cr-1Mo steel adequately. In this constitutive model, an applied stress consists of a backstress, an overstress and an aging stress which shows negative strain rate dependency. Each stress component was measured by strain rate change tests and strain dip tests, and material constants were systematically determined based on these measurements. To evaluate the validity of the constitutive model, it was applied to analysis of inelastic deformation behavior under various loading conditions. It was found out that the constitutive model was successful in describing the inelastic behavior of the steel precisely. (author)