[Purpose] The purpose of this study was to examine the association between muscle-strengthening exercises applied to the knee extensor muscles and the maintenance of standing balance in both, the anteroposterior and mediolateral directions in patients who had undergone total knee replacement. [Subjects and Methods] Thirty patients who underwent total knee replacement with bilateral artificial joints participated in this study. During the eight-week study period, the load on the knee extensors was gradually increased, and the standing balance ability was measured by differentiating the anteroposterior and mediolateral directions both, before and after the experimental period. [Results] In both, the anteroposterior and the mediolateral directions, there were statistically significant increases after the eight-week experiment, with a 29% increase in standing balance maintenance in the anteroposterior direction and a 22% increase in the mediolateral direction. [Conclusion] In patients who underwent bilateral total knee replacement, strengthening exercises applied to the knee extensor muscles with gradually increasing load positively affected standing balance in both anteroposterior and mediolateral directions.