Two patients with surgically resected biliary cystadenocarcinoma are presented. Both were asymptomatic and the cancer was incidentally found by ultrasonography (US). In the first case, a huge multilocular tumor (21 X 15 cm in diameter) having many papillary projections and septa within it and small daughter lesions occupied both the right anterior and left medial areas of the liver. They were clearly demonstrated on US and computed tomography (CT). Angiography disclosed tumor vessels in some area of the lesion, these features strongly suggested cystadenocarcinoma. The second case had a solid mass (7 X 7 cm) in the left hepatic lobe, in which many septal structures within the lesion were seen on enhanced CT and light dot like stains were recognized on angiography. The former findings coincided with the internal gross feature of the resected specimen. Both patients are doing well 8 months and 1 year and 6 months after operation, respectively.