Background: osteoarthritis, the most common form of arthritis, is a chronic disease characterized by slow degradation of cartilage, pain, and increasing disability. Objective: to study the effect of shock wave therapy in treatment of primary knee osteoarthritis. Patients and Methods: thirty patients with primary knee osteoarthritis were classified equally into 2 groups according to the line of treatment; Group I received extra-corporeal shock wave therapy and Group II received continuous ultrasonic waves. Patients were evaluated for pain using visual analogue scale, active range of motion, and physical and functional assessment. Bilateral anteroposterior weight bearing radiographs were done for all patients before treatment and degree of osteoarthritis was assessed by Kallgren and Lawrence Radiographic criteria. Results: there was significant improvement in group I more than group II (as regard to pain assessed by visual analogue scale (VAS) after treatment (p=0.039) and in follow up (p <0.001). There was significant improvement in morning stiffness in both groups with insignificant difference between both them. Regarding active range of motion (ROM), there was significant improvement in flexion in both groups with significant difference between both groups before and after treatment (p =0.001) and in follow up (p <0.001). Regarding chair stand test, there was significant improvement in both groups with in significant difference between them. Regarding stair climb test (SCT), there was significant improvement in both groups with insignificant difference between them. Conclusions: shock wave had an effect in treatment of primary knee OA as a new modality for improving clinical and functional performance.