Most gallbladder carcinomas are adenocarcinomas, of which mucinous carcinoma (MC) is a rare pathologic subtype. Signet ring cells are seldom found in MCs. We report an extremely rare case of gallbladder MC with signet ring cells. This is the first radiological case report about this rare type of histologic entity with detailed discussion of imaging findings in the English literature. In addition to the features of MC, linitis plastica-like invasion, which is the key feature of signet ring cells, was confirmed by both imaging and histopathologic analysis. Furthermore, radiologists should know how the imaging findings of MC differ from those of other major subtypes of adenocarcinoma, as there is a risk of delays in diagnosis and underestimation of tumor spread.