Mesenchymal hamartoma of the liver is a cystic benign liver mass occurring in children. Diagnostic confusion with hepatoblastoma may arise when a-feto-protein (AFP) level is elevated. We report an extremely rare case of mesenchymal hamartoma in an 11-month-old boy. Serum AFP was elevated and fine-needle aspiration biopsy suggested the lesion as hepatoblastoma, so he received preoperative chemotherapy. At the end of the preoperative chemotherapy, the tumor size and AFP level decreased. A right hepatectomy was performed. The pathologic examination of the specimen revealed mesenchymal hamartoma. Mesenchymal hamartoma of the liver with increased serum AFP levels may mimic hepatoblastoma if a cytological examination samples only the hepatocellular component of mesenchymal hamartoma. According to our knowledge, this is the first case of the mesenchymal hamartoma of the liver, which showed reduction in serum levels of AFP and involution of the tumor size by preoperative chemotherapy.