The purpose of this study was to investigate the effect of 10 weeks water exercise programme in the middle aged obese women with knee osteoarthritis. Subjects were 12 obese women with mean of 57 years of age, 156 cm height and 66.5 kg body weight. The water exercise programme consists of aquatic aerobic exercises with rating of perceived exertion 13-15 and 2 sets of 10 reps of aquatic resistance exercise. Body composition, muscular strength, muscular endurance, flexibility and balance were measured before and after the water exercise treatment. And also subjective pains before and after the treatment of water exercises were measured using Visual Analogue Scale. Data were processed using SPSS V.13.0 program to obtain mean and SD values of the measurements. Mean different measurement between the pre- and post-tests within the group was verified through paired t test. There were significant differences between pre and postwater exercise in body mass (65.9±7.4 kg vs 64.0±6.8 kg), body mass index (27±3 kg/m2 vs 26±3 kg/m2), % body fat (36.4% vs 35.4%) and body fat mass. The water exercise programme alleviated the subjective pain (6±2 vs 3±2) of obese patients who were suffering osteoarthritis of the knee by improving those patients' muscular strength (53±10 kg vs 57±2 kg), muscular endurance (6±6 reps vs 12±7 reps), flexibility (12±6 s vs 16±6 s) and balance (8.9±6.9 s vs 17.9±12.3 s). This also led to positive influences on the patients' daily life activities. In conclusion, water exercise programme would be effective in variation of physical ability, body composition and pain relief of obese patients who have osteoarthritis in the knee.