A case of spontaneous rupture of the urachal leiomyosarcoma in a 12-year-old boy is presented. This is of interest because massive hemoperitoneum due to spontaneous rupture of the urachal leiomyosarcoma is remarkably rare. We diagnosed based on histopathological features. Partial cystectomy and adjuvant chemo-radiation therapy was done with no sign of local recurrence or metastasis until 6 months after the operation.