20 subjects with symptomatic medial compartment knee OA, with grade 2 to 4 on Kellgren and Lawrence scale, and showing willing to wear a functional knee brace will be recruited into this study. Another 20 subjects with comparable body height, weight, and sex will be served as a control group. All of the subjects received 4 weeks' rehabilitation treatment (3 times a week). VAS pain score, WOMAC index, and SF-36 will be evaluated before the treatment, and 1 month, and 3 months after the start of treatment. Patients' satisfaction will be evaluated at 1 month, and 3 months after start of treatment. Patients' compliance and any adverse events due to wearing of the functional knee brace will also be reported. A 2-by-3, 2-way mixed-model analysis of variance, which had 1 between-subject factor (group: knee brace + PT and PT only) and 1 within subject factor (evaluation time:T0, T1, T2) , was performed. Pair-wise comparisons between groups were performed using an independent t test (if in normal distribution) or Mann-Whitney U test (if not in normal distribution). Investigators hypothesize that addition of a functional knee brace would improve rehabilitation outcome in subjects with knee OA.