A 9-year-old girl was diagnosed with primary alveolar soft part sarcoma of the bladder after imaging examinations and transurethral resection (TUR) of the bladder tumor. As a positive surgical margin of the TUR indicated residual tumor cells, we performed a cystourethrectomy to remove the tumor. A continent urinary reservoir for self-catheterization was constructed using the Mainz pouch technique, and an abdominal (umbilical) continent catheterizable stoma using the appendix was performed. For 2.5 years postoperatively, the patient remained free of local recurrence and distant metastasis. The patient's clinical course has been favorable, with good management of clean intermittent self-catheterization.