Extraskeletal osteosarcoma (ESOS) is a very rare entity among renal malignancies. There are few reports of renal ESOS in the database. Renal ESOS was found to have a high rate of local recurrence and distant metastasis. In most reports, the overall survival of patients was less than 1 year. We present a 51-year-old man who presented with gross hematuria and a clinical diagnosis of a staghorn stone in the left kidney. He underwent radical nephrectomy. The pathologic diagnosis of osteosarcoma was evident.