We report a case of primary leiomyoma of the liver. A 71-year-old man was admitted for investigation of a mass lesion in his liver, detected on ultrasonography. Computed tomography (CT) showed a solid tumor, 3 cm in diameter, in the caudate lobe of the liver. He underwent partial hepatectomy, and histological findings of the resected specimen revealed the proliferation of spindle cells, which formed a pattern of interlacing bundles, without any evidence of malignancy. The tumor cells were not immunoreactive to c-kit or S-100, but they were immunoreactive to alpha-smooth muscle actin. No other lesion was found elsewhere in the body. Thus, the tumor was diagnosed as a primary leiomyoma of the liver.