Background: Knee osteoarthritis is the most degenerative joint disease which can consequently cause a defect in balance control. Controlling the balance is necessary to prevent physical and psychological damages. This study aimed to investigate the effect of Mulligan mobilization technique on static and dynamic balances in patients with moderate to severe knee osteoarthritis. Methods: In a randomized controlled clinical trial, 31 patients with moderate to severe knee osteoarthritis were included and then assigned randomly into two groups of treatment (16 patients) and control (15 patients). Static and dynamic balances and pain score were evaluated in these patients once before and once after 10 sessions of treatment. Independent t-test and paired t-test were used for statistical analysis. The level of statistical significance was set at p < 0.05. Results: Pain significantly decreased in both groups after intervention (P<0.001). Pain reduction in the treatment group was significantly more than that of the control group (P=0.005). A significant improvement was found in static (P=0.01) and dynamic balances (P=0.006) after performing the intervention in the treatment group. Additionally, there was a greater improvement in static (P=0.04) and dynamic balances (P=0.02) in the treatment group compared to the control group. Conclusions: The results of the present study reveal that Mulligan mobilization technique could improve balance in patient with moderate and severe knee osteoarthritis.