Intracystic slow bleeding is very difficult to diagnose using conventional sonography; consequently, a new sonographic technique has been sought. We present a histologically proven hepatobiliary cystadenoma with intracystic bleeding in which contrast-enhanced sonography (CEUS) showed microbubbles oozing from the cyst wall into the cystic cavity 10 minutes after intravenous injection of contrast medium. CEUS is an important diagnostic tool for diagnosing liver tumors, but the CEUS finding of slow intracystic bleeding has not been reported. Our observation suggests that this technique may be a new diagnostic tool for this purpose.