Serous cystadenoma of the pancreas, also known as microcystic adenoma or glycogen-rich cystadenoma, is an unusually benign tumor. It is usually large and composed microscopically of many small cysts lined by small, cuboidal or flattened cells containing abundant glycogen. It has been suggested that serous cystadenoma probably arise from the ductular cells or centroacinar cells. Herein, we report on a case of serous cystadenoma of the pancreas in a 55-year-old female. The tumor, measuring 13.5x11.5x10.0 cm, was located in the head of the pancreas and the cut surface revealed a sponge-like appearance due to innumerable tiny cysts containing clear serous fluid. Microscopic analysis showed cystic spaces lined by cuboidal cells with intracytoplasmic glycogen.