Prepubertal Sertoli cell tumor of testis is very rare and most of them are benign. The choice of treatment is radical orchiectomy but careful follow-up for possible retroperitoneal spread is appropriate. We report a rare case of Sertoli cell tumor of testis in a 8-year-old boy. His chief complaint was a painless left testicular swelling from birth. Serum levels of tumor markers were within normal limits. Radical orchiectomy was performed, and cut surface of testis was yellowish and was completely displaced by lobulated tumor mass. Postoperative CT and chest x-ray showed no evidence of metastasis. The patient is alive without evidence of disease for 8 months postoperatively.