The aim of this study was to compare the effects of an intervention involving physical practice combined with motor imagery and physical practice alone on swimming performance for fifty-yard freestyle. Forty-five male and female high school swimmers were participants on two different high school teams. One team was the treatment group, which included the participants partaking in both motor imagery and physical practice. The other team served as the age matched control group, and the swimmers participated in physical practice only. The combined practice group performed motor imagery three times per week and physical practice five times per week. The physical practice only group performed physical practice five times per week. Each group performed their respective tasks for 9-weeks. Pre-, half-point, and post-tests consisted of a timed fifty-yard freestyle. The treatment group produced significantly faster times on the percent change in swim time scores in comparison to the control group for the half-time to post-time and pre-time to post-time score (p=.000). The treatment group also produced better performances on the pre-time to half-time scores, however, the results were not statistically significant (p = .009). Findings, therefore, support the effectiveness of motor imagery in enhancing swim performance, when combined with physical practice.