In an attempt to investigate the effect of a muscle strengthening exercise program on muscle strength, pain, depression, self-efficacy and quality of life of patients with knee osteoarthritis, a pre-experiment, one group pre-test and post-test design, was planned. Muscle strengthening exercise was carried out from May 22 through August 14, 1995 at isokinetic exercise room in rehabilitation department of University Hospital in Taejon. The subjects were seven female clients conveniently sampled from University Hospital located in Taejon, between 39 and 61 years of age, who had a osteoarthritis in knee. Muscle strengthening exercise program was composed of three sessions per week, one isokinetic exercise at angular velocity of 60degrees and 180degrees with Cybex isokinetic dynamometer and two resistance home exercise sessions with elastic band. Data were analyzed with frequency, percentage of change, Friedman test, Duncan test using SAS program. Results were obtained as follows: 1) Flexion and extension muscle strength at angular velocity of 60degrees and 180degrees were increased after 12weeks' exercise than those of before experiment. But exept flexion muscle strength at angular velocity of 180degrees (F=3.34, P=0.0261), there was no statistically significant difference among muscle strengths, which is measured every 3 weeks. 2) Pain was decreased after 6weeks' exercise than that of before experiment, and after 12weeks' exercise than that of 6weeks' exercise. There was statistically significant difference(F=4.28, P= 0.0396). 3) Depression was increased after 6weeks' exercise than that of before experiment, and after 12weeks' execise than that of 6weeks' exercise. There was no statistically significant difference between before experiment and after 6weeks' exercise. But, there was statistically significant difference between after 6weeks' exercise and 12weeks' exercise (F=9.38, P=0.0035). 4) Self-efficacy was decreased after 6weeks' exercise than that of before exercise. But, it was increased after 12weeks' exercise than that of before exercise and after 6weeks' exercise. But there was no statistically significant difference (F=1.46, P=0.2706). 5) Quality of life was increased after Gweeks' exercise than that of before exercise, and after 6weeks' exercise than that of 12weeks' exercise. But there was no statistically significant differ-ence(F=1.06, P=0.3816). Thus, the significant of muscle strengthening exercise for the improvement of muscle strength, pain, depression, is verified. But, this study was a preexperiment with small size subjects. So, controlled experimental study is necessary to determine the effect of this muscle strengthening exercise program on muscle strength, pain, depression, self-efficacy, and quality of life of patients with knee osteoarthritis.