Introduction: This study aimed to investigate the effects of various exercises on quadriceps femoris muscle and on pain, strength, function, and balance in female patients with bilateral knee osteoarthritis (OA). Methods: Forty-five female patients aged 40-65 years were diagnosed with bilateral knee OA according to the American College of Rheumatology criteria and randomized into three groups. The pain and function of the patients in each group were evaluated by the visual analog scale and Western Ontario and McMaster Universities Osteoarthritis Index questionnaires. Muscle strength and endurance were measured with the Isokinetic System Cybex 350, and balance was evaluated with Biodex Balance System SD. Group 1 performed a home-based isometric exercise program, while groups 2 and 3 performed strength and endurance exercises, for 4 days per week for 6 weeks. Results: At week 6, only the activity pain scores decreased in group 1, whereas rest, night, and activity pain scores decreased significantly in groups 2 and 3 (p<0.001, p<0.01 and p<0.001, respectively). Significant improvements in physical functions were found in each group (p<0.001). The isokinetic muscle strength for knee extensors increased significantly in groups 2 and 3 (p<0.001, p<0.01, respectively). The balance scores of groups 2 and 3 were improved at certain positions (p<0.001, p<0.05, respectively). Conclusion: Isometric exercises are widely used in the treatment of patients with knee OA. However, high-intensity isotonic exercises is recommended because of the shorter time of intervention for improving muscle strength, slowing the progression of the disease, and reducing the future risk of falling by improving balance.