Background Hypertrophic scars cause aesthetic concerns and negatively affect the quality of life. A gold standard treatment for hypertrophic scars has not been established due to various responses of modalities. Extracorporeal shock wave therapy (ESWT) is a noninvasive and affects scar remodeling by fibroblast regulation. This study investigated the effectiveness of ESWT for hypertrophic scars. Methods Twenty-nine patients were enrolled. All patients underwent ESWT once a week for 6 consecutive weeks. Their scars were assessed using the Patient and Observer Scar Assessment Scale (POSAS), erythema index, melanin index, and scar pliability before treatment and again 4 weeks after treatment completion. Results Thirty-four hypertrophic scars in this study had persisted for between 6 months and 30 years. Most scars developed after surgical incision (55.88%). The chest and upper extremities were the predominant areas of occurrence (35.29% each). Most of the POSAS subscales and total scores were significantly improved 4 weeks after treatment (p < 0.05). Furthermore, the pain, itching, and pigmentation subscale were improved. The pliability, melanin index, and erythema index were also improved, but without significance. The patients were satisfied with the results and symptoms alleviation, although subjective score changes were insignificant. No serious adverse events were found. The patients reported pruritus in 62.5% and good pain tolerance in 37.5%. Subgroup analyses found no differences in scar etiologies or properties at different parts of the body. Conclusion The ESWT is a modality for hypertrophic scar treatment with promising results. Most of POSAS subscales were significantly improved.