The purpose of the current study was to examine the effects of motivational self-talk on self-efficacy and performance. Participants were 46 young tennis players (mean age 13.26, SD 1.96 years). The experiment was completed in five sessions. In the first session, participants performed a forehand drive task. Subsequently, they were divided into an experimental and a control group. Both groups followed the same training protocol for three sessions, with the experimental group practicing self-talk. In the final session, participants repeated the forehand drive task, with participants in the experimental group using motivational self-talk. Mixed model ANOVAs revealed significant group by time interactions for self-efficacy (p < .05) and performance (p < .01). Follow-up comparisons showed that self-efficacy and performance of the experimental group increased significantly (p < .01), whereas self-efficacy and performance of the control group had no significant changes. Furthermore, correlation analysis showed that increases in self-efficacy were positively related to increases in performance (p < .05). The results of the study suggest that increases in self-efficacy may be a viable mechanism explaining the facilitating effects of self-talk on performance.