Background : Nonsteroidal anti–inflammatory drugs (NSAIDs) have been recommended for management of post-operative pain and their opioid-sparing effect has been proved in various situation. One of the indications of specific cyclooxygenase-2 inhibitor NSAIDS, Rofecoxib, is to alleviate post-operative pain but the analgesic efficacy combined. We administered Rofecoxib in pre-emptive fashion to patients undergoing arthroscopic anterior cruciate ligament (ACL) reconstruction. Method : A double blind, randomized controlled trial was conducted. Forty patients scheduled for arthroscopic ACL reconstruction were enrolled in the study. They were allocated into 2 groups, 20 of each, receiving either oral 50 mg of Rofecoxib or placebo 1 hour preoperatively. Spinal anesthesia was perfomed with 0.5% heavy bupivacaine and morphine in every patients. Intravenous morphine via Patient Controlled Analgesia (PCA) was available for all patients. Time of first dose of morphine, total amount of morphine requirement, pain scores, adverse reactions were recorded during the first 24 hours. Result : The Rofecoxib group has significantly longer average time to the first analgesic requirement, 1004 minutes as compare to 720 minutes in the control group (p = 0.02). Accumulated intravenous morphine dose was significantly less in the Rofecoxib group than that in the control group, 3.75 mg vs 11.9 mg (p<0.0001). Pain scores were significantly lower in the Rofecoxib group than that in the control group (p = 0.0048). Conclusion : Preemptive Rofecoxib for arthroscopic ACL reconstruction combined with intrathecal anesthesia demonstrates an opioid sparing effect and is an effective pain management method by providing longer duration of analgesia and enhancing analgesic effects through the first 27- hour period without any adverse effects.