PURPOSE To assess proper soft tissue balancing of the varus arthritic knee between posterior oblique ligament (POL) release group and superficial medial collateral ligament (SMCL) release group. MATERIALS AND METHODS This retrospective study was performed on 186 patients who underwent minimally invasive surgery (MIS) total knee arthroplasty (TKA) from January 2011 to December 2011. Eighty-three patients were in the group of SMCL release and 103 patients were in the POL release group. We intended to use a 10 mm polyethylene insert (PE) during TKA, and retrospectively compared the actual thickness of PE between POL release group and SMCL release group. RESULTS The mean PE thickness was 10.59±1.3 mm (range, 8 to 15 mm) in POL group and 11.88±1.8 mm (range, 10 to 18 mm) in SMCL group (p=0.001). We found a significant difference in the mean PE thickness between POL release group and SMCL release group. CONCLUSIONS POL and deep MCL releases in MIS-TKA would be beneficial for varus deformity correction in the osteoarthritic knee.