PURPOSE: To evaluate the short-term postoperative results of minimally invasive Unicompartmental Knee Arthroplasty(UKA) and to analysis the early postoperative complications. MATERIALS AND METHODS: 241 cases of UKA have been performed since January 2002 and followed up for average 27.3 months. Most of cases were medial compartment degenerative arthritis. All operative procedures were performed through minimally invasive technique. Clinical assessments were carried out using the Knee Society Score (KSS) rating system. RESULTS: The average knee score and the knee function score were improved from 55.4 and 55.4 points preoperatively to 89.3 and 84.9 points at final follow up. The average range of knee motion was 128.4 degrees preoperatively and recovered to 133.0 degrees at final follow up. Average preoperative tibiofemoral angle was 0.2 degrees of varus, which changed to 5.5 degrees of valgus at final follow up. Early complications after minimally invasive UKA were seen in 14 cases, 13 of which were occured within the first year. There were 4 polyethylene insert dislocation, 3 periprosthetic fracture, 2 femoral component loosening, 3 MCL injury and 1 infection. We also experienced 2 partial capsular rupture, 1 remained cement fragment in the joint and 1 impingement between osteophyte and stem. Two femoral component loosening and 1 MCL injury were combined with bearing dislocation. CONCLUSION: The short-term postoperative results of minimally invasive UKA were clinically satisfactory for improvement of knee score, function score and in the recovery of knee motion. The complication rate of UKA was relative low, but mostly caused by errors in surgical technique. Accurate surgical technique and enough experience were needed to improve clinical results and reduce the complications. When complications have occurred, better results are expected by more appropriate treatment for the cause of the complications.