PURPOSE: To evaluate the minimum 5-year mid-term clinical and radiological results of minimally invasive surgery total knee arthroplasty (MIS-TKA) using a mini-keel modular tibia component. MATERIALS AND METHODS: We retrospectively evaluated 254 patients (361 cases) who underwent MIS-TKA between 2005 and 2006. The latest clinical and radiological assessments were done in 168 cases that had been followed on an outpatient basis for more than 5 postoperative years. Clinical results were assessed using the Hospital for Special Surgery (HSS) score and Knee Society score. Radiological evaluation included measurements of knee alignment. RESULTS: The average postoperative knee range of motion and HSS score were 134.3degrees+/-12.4degrees and 92.7degrees+/-7.0degrees, respectively. The average postoperative femorotibial angle and tibial component alignment angle were 5.2degrees+/-1.7degrees valgus and 90.2degrees+/-1.6degrees, respectively. The average tibial component posterior inclination was 4.8degrees+/-2.1degrees. The percentage of cases with tibial component alignment angle of 90degrees+/-3degrees was 96.1%, and that with the femorotibial angle of 6degrees+/-3degrees valgus was 94.0%. Radiolucent lines were observed in 20 cases (12.0%): around the femur, tibia, and patella in 14 cases, 10 cases, and 1 case, respectively. However, they were less than 2 mm and non-progressive in all cases. The survival rate was 99.4% and there was no implant-related revision. CONCLUSIONS: MIS-TKA using a mini-keel modular tibial plate showed satisfactory results, a high survival rate, and excellent clinical and radiological results in the mid-term follow-up.