Actinomycosis is a chronic suppurative infection caused by Actinomyces, a filamentous, grampositive, anaerobic bacterium that is a normal inhabitant of the oral cavity and gastrointestinal tract. Actinomycosis of the biliary duct is very rare and the pathogenesis of this infection is poorly understood. We report here on a case of actinomycosis in the intrahepatic bile duct that was superimposed on hepatolithiasis. A 55-year-old woman presented with epigastric discomfort and episodic upper abdominal pain for 1 year. The radiologic findings revealed multiple hepatolithiasis and cholelithiasis. On performing left lateral segmentectomy of the liver, the markedly dilated intrahepatic bile duct contained several brown pigmented stones, and periductal chronic inflammation with fibrosis and proliferation of the bile ductules were observed. In addition to the intrahepatic stones, there were sulfur granules with neutrophilic infiltration and necrotic debris. The gram stain and methenamine silver stain revealed tangled filamentous and branching bacteria, which were consistent with Actinomyces. Acid-fast staining result was negative and no malignancy was detected.