Objective: To study the effect of the muscle strength exercise on knee osteoarthritic patients with muscle weakness. Method: The isokinetic parameters of pre and post muscle strength exercise were compared on 26 involved limbs and the parameters of pre and post passive motion on 19 involved limbs as well. Result: Although muscle strength increased in both groups, muscle strength exercise group was more successful on reducing muscle weakness. Conclusion: Muscle strength exercise can reduce muscle inhibition of osteoarthritic patients through recruitment.