This study aimed to compare the effects of action potential simulation with low level LASER in reducing pain and improving function of women with knee osteoarthrosis. This single-blind, randomized clinical trial was carried out in Zahedan University of Medical Sciences, in 2009. Thirty patients with knee Osteoarthrosis were recruited through simple non-probability sampling. Patients were selected based on following inclusion criteria: Age between 14 and 40, having knee pain according to Altman’s classification, lack of regular exercise (non-professional or professional) over the past 10 years, not regular or irregular (5 times per week) of analgesics and steroidal and non-steroidal anti-inflammatory drugs within 2 months prior to study entry. Patients were excluded if they had insufficient treatment, using other therapeutic modalities during the study, trauma, doing surgery during the study, exacerbation of symptoms following the intervention, patients who have had a history of knee surgery, intra-articular injections in the past 6 months; and lower extremity fracture in last 3 months. Patients were randomly assigned to either a low-level LASER group (N=15) or an action potential simulation group (APS) (N=15). In LASER group, a low-level Ga-As LASER was applied with 5 KHz frequency, a 100 mW point probe (average power), wavelength 905 nm, pulse duration 200 ns, 9 J/cm2 dosages per minute, for 6 minutes per session. In action potential simulation group, action potential simulation was applied with intensity of 1mA, 150 Hz frequency, for 16 minutes per session. Both groups received exercises including strengthening of quadriceps, adductors of the hip, and stretching of iliotibial band, buttock, calf and hamstring muscles and hot pack. A 16-session treatment program, during 4 weeks, 4 sessions per week was performed for both groups. Before and after intervention, we measured pain through Visual Analog Scale (VAS) (ordinal), function with Knee and Osteoarthritis Outcome Score (KOOS), and range of knee flexion with goniometer (degree), stiffness, pain and physical function with Western Ontario and McMaster Universities Index (WOMAC) (Ordinal) and atrophy and swelling with tape measure (centimeter).