Purpose: The purpose of this study was to investigate the effects of extracorporeal shock-wave therapy (ESWT) on pain, grip strength, and upper-extremity function in patients diagnosed with lateral epicondylitis and to provide an effective intervention method for lateral epicondylitis. Methods: Twenty patients with lateral epicondylitis were randomly assigned to the ESWT group (n = 10) and the stretching exercise group (n = 10). Interventions in both groups were performed six times twice a week for three weeks. The visible analog scale (VAS) was used to measure pain change. A dynamometer was used to measure grip strength (GS). Patient-rated tennis elbow evaluation (PRTEE) was used to measure the upper-extremity function. Results: There were significant differences in pain, grip strength, and upper-extremity function in both groups before and after intervention (p < 0.05). There were also significant differences in pain, grip strength, and upper-extremity function between the groups after intervention (p < 0.05). Conclusion: This study showed very positive improvement in pain, grip strength, and upper-extremity function after ESWT in patients with lateral epicondylitis. Therefore, ESWT can be recommended for patients with lateral epicondylitis.