Objective To investigate the short- and mid-term effectiveness of unicompartmental knee arthroplasty (UKA) for post-traumatic arthritis (PTA) of knee. Methods The clinical data of 30 patients with PTA of unilateral knee between March 2014 and September 2021 was retrospectively analyzed. There were 14 males and 16 females with an average of 64.5 years (range, 33-81 years). The average body mass index was 26.7 kg/m2 (range, 19.8-35.6 kg/m2). The types of injuries that caused PTA included intra-articular fracture in 16 cases, extra-articular fracture in 8 cases, and soft tissue injury in 6 cases. The initial injuries were treated by conservative therapy in 12 cases and by surgical therapy in 18 cases. Ten cases were medial compartment osteoarthritis and 20 cases were lateral compartment osteoarthritis. According to Kellgren-Lawrence staging, there were 19 cases of grade Ⅲ and 11 cases of grade Ⅳ. The operative time, the length of hospital stay, complications, and subjective satisfaction were recorded. The Oxford Knee Function Score (OKS), Hospital for Special Surgery (HSS) score, and knee range of motion (ROM) were used to evaluate knee function. Weight-bearing X-ray films were taken to measure the femoro-tibial angle (FTA) and to assess alignment correction of the lower limb. Results The operative time ranged from 50 to 95 minutes (mean, 63.7 minutes), the length of hospital stay ranged from 3 to 8 days (mean, 6.9 days). Superficial infection occurred in 2 patients, while the remaining incisions healed by first intention. There was no deep vein thrombosis or neurovascular injury. All patients were followed up 17-109 months (median, 70 months). At last follow-up, OKS score, HSS score, and ROM in 30 cases significantly improved when compared with those before operation (P<0.05). Lower limb alignment was significantly corrected and there was significant difference in FTA of the varus and valgus knees between pre- and post-operation (P<0.05). The patient satisfaction rate was 86.7% (26/30). Two cases developed contralateral osteoarthritis progression during follow-up. No bearing dislocation, prosthesis loosening or sinking occurred and none required further revision. Conclusion For patients with PTA of knee, UKA can obtain definite short- and mid-term effectiveness with high patient satisfaction.