Purpose: The purpose of this study was to determine the effects of a lower extremity exercise program on muscle strength and flexibility in women with knee osteoarthritis. Method: This study was conducted using a non-equivalent control group pretest-posttest design. The participants were 35 women with knee osteoarthritis. The experimental group performed the lower extremity exercise program, which was an adapted BeHaS exercise program developed by Kim(2006). It consisted of approximately 65-130 minutes per one session, two days a week, for twelve weeks. Lower extremity muscle strength was measured by the Seated Leg Press Machine (TY-H2217, made in Korea), back muscle strength by back muscle strength scale (TKK 5402, made in Japan) and flexibility, by Sit and Reach tester (01285, U.S.A). Data were gathered from September 2005 to March 2006. Frequency, $X^2$ test and t-test were used to analyze the data. SPSS Win 11.0 was used to assist analysis. For normal distribution of data, Kolmogorov-Smirnov test was done. Results: There were statistical differences in the mean strength of both legs together, strength in leg with more pain(p=.044; p=.046), sit and standing time (p=.007), and back strength (p=.021). Conclusion: Based on these results, it can be concluded that a lower extremity exercise program can help improve lower extremity muscle strength in women with osteoarthritis.