Biliary cystadenocarcinoma is a very rare malignant cystic tumor of the liver, which is often misdiagnosed due to a poor recognition of it. We report a case of a 60-year-old man with biliary cystadenocarcinoma with his real time contrast enhanced ultrasound (CEUS) characteristics compared to those of computed tomography (CT) and magnetic resonance imaging (MRI), which were correlated with the surgical and pathologic findings. Cystic wall enhancement, internal septations and intra-cystic solid portions in the arterial phase were observed on CEUS after contrast agent injection. The enhancement was washed out progressively and depicted as hypo-enhancement in the portal and late phases. CT revealed a large irregular cystic lesion in the left liver lobe with no clear septations and solid components. MRI showed an irregular cystic occupying lesion with septations.