A case of unusually hypermobile floating gallbladder in a 79-year-old woman with histologically distinct double cancers of the gallbladder is described. The patient presented with an abdominal cystic mass, which was palpable with easy mobility from the right lower quadrant practically to the left upper quadrant. Exploratory laparotomy was performed and the cystic mass was found to be a floating gallbladder. The cystic duct was elongated and obstructed, and had a long mesentery. After the operation, latent double cancers of the gallbladder were discovered on histopathological examination. The obstruction of the cystic duct was due to chronic inflammation and had resulted in hydrops of the gallbladder. This was suspected to have played an important role in the carcinogenesis. We believe that this is the first report of a floating gallbladder associated with double gallbladder cancers.