Calcification and ossification of colon cancer is frequently encountered, especially in the mucinous carcinoma. However, cartilage formation or enchondral ossification has rarely been described in human colon cancer. This report describes a case of a 59-year-old man with retroperitoneal metastasis of mucinous adenocarcinoma of colon, which showed a widespread heterotopic ossification through membranous or enchondral ossification. The ossification appeared in apposition to tumor cell nests and in the organized mucin pool. In our knowledge, this is the first case showing enchondral ossification in gastrointestinal carcinoma in Korea.