Objective To investigate the clinical efficacy of fixed-bearing unicompartmental knee arthroplasty in the treatment of medial compartment osteoarthritis in the elderly patients. Methods Thirty-eight elderly patients (14 males and 24 females, at an age of 66.0±5.6, ranging from 60 to 72 years) diagnosed of knee osteoarthritis in our department between January 2005 and March 2010 were enrolled in this study. Preoperative examination showed that most of them had pain in the medial joint space while standing and walking, and lateral X-ray of the knee joint suggested medial compartment osteoarthritis. All the patients received unicompartmental knee arthroplasty, and took postoperative rehabilitation. Results The operation time was (45.0±10.2)min, and no blood vessel and nerve damage, no incision infection and complication were observed. All incision acquired phase Ⅰ healing. All of the patients completed the followed-up of （102.0±12.2）months (71-133 months), and no death or withdrawal occurred during the period. At the end of follow-up, their Hospital for Special Surgery (HSS) score (91.8±17.9 vs 52.6±16.7), visual analogue scale (VAS) score for pain (1.8±0.9 vs 6.3±1.2), varus deformity (4.7°±0.9° vs 8.9°±1.6°), and range of motion (129.7°±36.8° vs 112.6°±23.5°) were greatly improved when compared with those before operation (P<0.05). Conclusion Fixed-bearing unicompartmental knee arthroplasty achieves good clinical efficacy in the treatment of medial compartment osteoarthritis in the elderly.