In this paper, a constitutive model for cemented clay is introduced. This model is designated as "Modified Structured Cam Clay (MSCC) model". In the model, the influence of cementation structure is incorporated into effective stress concept, yield function, hardening rule and plastic potential function to describe the mechanical behavior of cemented clay during strain-hardening and softening. The methodology of modeling the shear behavior of structured clay is simple, which is the same way as that of the other models of the Cam Clay family. The capability of the MSCC model is verified by comparing the simulated undrained shear response of cemented Ariake clay under various effective confining stresses and degrees of cementation with experimental data.