The purpose of this study was to evaluate the painrelief effect of intra-artieular morphine after knee arthroscopy. First, the authors selected 20 general anesthetic patients and divided them equally into 2 groups ; the control group, and the morphine group. Second, at the end of knee arthroscopy, we injected 1mg of preservative free morphine in 20ml normal saline solution into knee joint cavity of the morphine group, while we injected only 20ml normal saline solution to the control group. And tourniquet was inflated above knee joint for ten minutes after injection in each patient. Third, we measured changes of systolic arterial blood pressure(SABP), diastolic arterial blood pressure(DABP), heart rate(HR), and respiratory rate(RR) before operation and at 1, 2, 3, 4, 5, 6, 12, 24 hour after knee arthroscopy. Fourth, we also measured visual analogue scale(VAS), requirement of supplemental analgesics, and systemic side effects of morphine. The results were as follows ; 1. SABP, HR, RR were increased significantly(p<0.05) at 1 hour after intra-articular injection in control group, but SABP, DABP, HR, RR were not changed signifieantly in morphine group. 2. VAS was decreased significantly(p<0.05) in morphine group compared with conrol group at each period after intra-articular injection. 3. Supplemental analgesics were not required in morphine group at all. With these results, we could conclude that intra-articular morphine is effective for pain relief after knee arthroscopy without any side effect.