Primary rat hepatocytes formed cylindrical multicellular aggregates on a pressed sheet of polyurethane foam (pressed-PUF) as a culture substratum. The sheet was made up by pressing PUF during the process of foaming. The diameter and length of the hepatocyte cylindroid is approximately 200 ~ 500 μm and 500 μm ~ 2 mm, respectively. Its activities of liver specific functions (albumin secretion and ammonia metabolism) were equal to those of hepatocyte spheroids. These results indicated that hepatocytes cylindroid are a kind of organoid, and will provide a useful culture technique for high cell density culture.