The present invention provides a method for predicting an effectiveness of chemotherapy using an anticancer agent with high probability. The effectiveness is predicted based on a comparison of a parameter relating to CDK and/or CDK inhibitor in a tumor cell specimen obtained from a patient, with a corresponding threshold value to the parameter. The patient to be subjected this sensitivity prediction test of an anticancer agent is administered with the anticancer agent prior to removal of the tumor cell. The threshold is predetermined based on data of correlation between the selected parameter and anticancer agent therapy results obtained from a number of patients actually performed the therapy. Accordingly, the predicting method can provide information useful for determining whether to perform the chemotherapy to individual patients.