Sarcomatoid carcinoma of the urinary bladder is a rare malignant neoplasm in which the tumor consists of both carcinomatous and sarcomatous elements. In Korea, only 1 case of bladder and renal pelvis primary sarcomatoid carcinoma and 4 cases of carcinosarcoma involving the bladder have been reported. Recently, we experienced a case of sarcomatoid carcinoma of the bladder in a 78-year-old male patient experiencing severe gross hematuria. An ultrasound demonstrated a broad-based tumor 4.5×3.6 cm in size on the lateral side of the right ureteral orifice in the bladder dome. Under the diagnosis of a bladder tumor, transurethral resection of the bladder tumor (TURBT) was performed. A subsequent histological examination of the biopsy specimens showed both malignant mesenchymal and epithelial elements. As a result, the tumor was pathologically confirmed as a primary sarcomatoid carcinoma of the urinary bladder.