Abstract: This paper deals with the experimental study of fracture toughness of mode Ⅰ,mode Ⅱ and mixed mode for hard rocks. According to the results obtained by 3 types of fracturing tests a fracture toughness curve was given for evaluation of crystalline rocks, such as syenite and basalt. The value of fracture toughness seems to be dependent upon the mineral composition, texture and structure, including some minor discontinuity. Moreover, a close relationship between the frcture toughness and the velocity of sound wave jn rocks was also found by laboratory experiment.