OBJECTIVE: Retrospective analysis to compare the effect and complication of epidural patient-controlled analgesia (epidural PCA) with intravenous patient-controlled analgesia (IV PCA) for the treatment of the post-operative pain after posterior lumbar instrumented fusion. METHODS: Sixty patients who underwent posterior lumbar instrumented fusion for degenerative lumbar disease at our institution from September 2007 to January 2008 were enrolled in this study. Out of sixty patients, thirty patients received IV PCA group and thirty patients received epidural PCA group. The pain scale was measured by the visual analogue scale (VAS) score. RESULTS: There were no significant difference between IV PCA group and epidural PCA group on the PCA related complications (p=0.7168). Ten patients in IV PCA group and six patients in epidural PCA group showed PCA related complications. Also, there were no significant differences in reduction of VAS score between two groups on postoperative 2 hours (p=0.9618) and 6 hours (p=0.0744). However, postoperative 12 hours, 24 hours and 48 hours showed the significant differences as mean of reduction of VAS score (p=0.0069, 0.0165, 0.0058 respectively). CONCLUSION: The epidural PCA is more effective method to control the post-operative pain than IV PCA after 12 hours of spinal fusion operation. However, during the first twelve hours after operation, there were no differences between IV PCA and epidural PCA.