Background: Knee osteoarthritis (KOA) contributes to disability more than other type of arthritis because it affects on the elderly patients' daily living activity level and increases the level of dependency on their caregivers. Walking is a simple and safe form of isotonic exercise that can be effectively used to decrease knee joint pain, enhance the joint function. Objective: evaluate the effect of aerobic walking program on pain and function of elderly patients with KOA. Methods: randomized control research design was used in this study. Purposive sample of the present study composed of 66 elderly patients of both sexes who met inclusion criteria and divided alternatively into two equal groups. Results: before the application of aerobic walking program the result indicates that, WOMAC average score in study group was 78.2±13 and for control group was 79±15.6 with no significant difference between both groups P= 0.609. After application of aerobic walking program, a significant improvement in mean total WOMAC score was found in study group (27.6±14.5) than control group (79.8±15.9) (P= 0.000). Conclusion: Based on findings of the current study, we can conclude that aerobic walking program was successful in improvement of function and decreasing knee pain.