Relief of postoperative pain after arthroscopic knee surgery is important to promote early rehabilitation of patients. This study was aimed to compare the analgesic effects of bupivacaine and morphine injected into the knee after arthroscopic surgery. In a double-blind, randomized trial, we studied 60 patients who received one of three injections at the end of surgery. The patients were randomly divided into three groups; group 1 received 25ml of 0.25% bupivacaine, group 2 received 5mg of morphine mixed with 25ml of 0.9% normal saline and group 3 received a mixture of 25ml of 0.25% bupivacaine and Smg of morphine. Postoperative pain was assessed using a 100-mm visual analog scale(VAS). We recorded the total number of injections of supplemental analgesics, and the occurrence of side effects of bupivacaine and morphine were monitored. In group 1, VAS was significantly lower than group 2 at one and two hours after injection, but it was higher than the other two groups after four hours. In group 2, VAS was significantly lower than group 1 after four hours and later, but it was higher than the other two groups at one and two hours after injection. In group 3, VAS was maintained low during early and late postoperative period. No side effect was found in all patients. We conclude that intra-articular bupivacaine decreases early postoperative pain, morphine decreases late postoperative pain, and the mixture of bupivacaine and morphine is the most effective in controlling the postoperative pain during early and late period.