This article reports five cases of colonic adenocarcinomas in a family group of captive Amur rat snake (Elaphe schrenckii) from the Réserve Africaine de Sigean, France. This tumor was detected in three females and two males, all adults, and accounted for 16% of causes of death of adults of this species at this institution from 1986 to 2013. Grossly, mild to marked thickening of the intestinal wall cranially to the cloaca was found in four cases; tan to yellow firm masses were noted in the distal intestinal wall in the other case. Microscopically, neoplasms were characterized by infiltrating, poorly circumscribed, and unencapsulated nests of epithelial cells. Marked anisokaryosis and anisocytosis were seen in all neoplasms. The etiology of the neoplasms was not determined, but the familial clustering suggests a common etiologic factor.