A quantitative way to predict the unconfined compressive strength of cement-mixed clays with a given organic content is proposed. The Yancheng lagoonal soft clays were used as an original clay to form cement-mixed clays through mixing with powder cement or slurry cement and organic matters. A series of tests were performed on the cement-mixed clays with various organic contents. A quantitative relationship is proposed between the strength ratio of the strength with a given organic content of y to the experimental strength with an organic content of y′ and the organic contents of y and y′ . The quantitative expression proposed can be effectively to predict quantitatively the effect of organic content on the unconfined compressive strength of cement-mixed clays within the organic contents of 5.5 %-17.5 %.