A method for evaluating the undrained shear strength of clay during the processes both primary and secondary compressions is proposed from a consideration of one-dimensional consolidation models with creep. A new stress parameter is defined to evaluate the stress change during all processes of consolidation, which is called “conversion stress”. An equation for estimating the increase in the strength during consolidation is formulated based on the conversion stress. The validity of the proposed method is investigated from direct comparison of the calculated results with the experi mental ones. The calculated values are in satisfactory agreement with the experimental ones, which is obtained by some kinds of test with remolded and undisturbed clays.