In order to evaluate the effects of cementation on the mechanical properties of cement-treated soil, a series of isotropic consolidation and undrained triaxial compression shear tests were performed for cement-treated specimens of Ariake clay, Akita sand, Rokko Masado and Toyoura sand. This paper evaluates factors affecting the shear strength of these cement-treated soils. The following conclusions are obtained: 1) Cement-treated soil has a normally consolidated line in e-ln p' space which depends on the mixing cement content. The consolidation yield stress, p'_y, of cement-treated soil increases with increasing cement content and initial specimen density. 2) Changes in cohesive strength due to cement-treatment can be represented by a tensile effective stress, p'_r. Strength properties can then be normalized by the augmented consolidation stress, (p'_c+p'_r). 3) The shear strength properties of quasi-overconsolidated clay can be represented by the yield stress ratio, R=(p'_y+p'_r)/(p'_c+p'_r). 4) The undrained shear strength of cement-treated soils can be represented as a power law relation of the yield stress ratio, R, and the augmented consolidation stress.