OBJECTIVE To investigate the effects of intra-articular injection of sodium hyaluronate in post-operation treatment of the knee. METHODS From January 1998 to February 2001, 4 ml of sodium hyaluronate injection was injected into the knee joint of the 134 cases at the end of arthroscope operation, or the 91 cases undergoing open operation of the knee at the time when the drain tube was removed (treatment group). Five days after operation, the hydrarthrosis was removed and 2 ml of sodium hyaluronate was injected into the knee joint. According to the patient’s condition, injection of sodium hyaluronate was performed once a week for several weeks. Clinical evaluation was made by evaluating pain visual analog scale (VAS) and painless range of movement (ROM) of the joint at every definite point of time. The 85 patients in control group used nothing at the same time. RESULTS The VAS score of patients in the treatment group was significant lower than that of the control group. The period to the maximal painless ROM of the joint was 6 days in the treatment group after open operation, while 9 days in the control group. CONCLUSION Sodium hyaluronate appears effective in relieving post-operation pain of the knee joint.