Introduction:Tennis elbow (Lateral Epicondylitis) is one the most common elbow and arm musculoskeletal disorders. About 1% to 3% of active population in modern societies suffer from tennis elbow. Tennis elbow is usually caused by repetitive activities of hand and wrist, especially wrist extension and forearm supination. This research aimed to study high and also medium power gallium arsenide (Ga-As) laser irradiation on improving pain and grip strength (functional mobility) in patients with tennis elbow. Materials and Methods:Thirty female [Mean(SD) age: 49(2.3) y] patients with acute tennis elbow were recruited for this study. The patients were randomly divided into two groups based on random allocation table. Group A (15 patients) had been received 10 J/cm 2 under a 0.5 W beam medium power Ga-As laser irradiation of 980 nm wave length. Group B (15 patients) had been received same energy density under 2 W beam high Ga-As laser irradiation with the same wavelength. Laser irradiation was performed on a 9 cm 2 surface of lateral elbow epicondyle based on Grid laser application technique. The patients were under treatment for 10 sessions every other day. The outcome measures of pain at rest and ring finger extension against loading, grip strength and hand function were recorded and analyzed in a pre-and post-setting. The pain severity was measured by VAS (Visual Analog Scale) and McGill questionnaire and upper extremity function was measured by DASH questionnaire.Results: Significant pain reduction was observed in resting position and ring finger extension against loading after application of both high and medium power (980 nm, 0.5-2 W) laser therapy (P<0.05) for 10 sessions. High power laser irradiation could also increase grip strength and mobility in patients with lateral epicondylitis (P<0.05). Conclusion:High and low power Ga-As laser irradiation may improve pain and grip strength in patients with acute tennis elbow.