In order to differentiate yolk sac type alpha fetoprotein (AFP) from hepatic‐type AFP, 5 yolk sac tumors (YSTs) and 6 hepatocellular carcinomas (HCCs) were examined immunohistochemically by the peroxidase antiperoxidase (PAP) method for AFP, and paradoxical concanavalin A (P Con A) staining, which has been reported to detect glycoprotein including AFP. In all 5 YSTs, AFP was negative for P Con A staining. On the other hand, AFP was strongly positive for the same staining in all 6 HCCs. A similar staining pattern for AFP was observed in human yolk sac endodermal cells and embryonal hepatocytes. Thus, it was clarified that yolk sac type AFP was unable to bind with Con A, in contrast with hepatic‐type AFP, on tissue sections. It was concluded that the PAP method for AFP and P Con A staining might facilitate the immunohistochemical differentiation of these two types of AFP, and that it would be usetul for clarifying the histogenesis of various AFP secreting tum