To assess the failure risk of high temperature structures, it is essential to obtain the creep fracture toughness of materials. In the present paper, Creep crack growth (CCG) tests for 2¼Cr1Mo steel have been carried out by utilizing the side grooved compact tension (CT) specimen and direct current (DC) electrical potential technique. The material parameter of creep fracture toughness, c mat K , were obtained from analysis of 11 CCG tests at temperatures of 500 and 565oC. It has been found that for 2¼Cr1Mo steel c mat K decreases with increasing time and increases with elevating temperature. For this reason, the value of c mat K at lower temperature or longer service time can be used to extract a conservative result in the high temperature defect assessment where the accurate value of c mat K is unavailable. It is also validated from this test that the proposed formula by Ainsworth et al can be adopted in practice.