The present invention provides a technique for dramatically extending the life of a plug used when rolling high-alloy-steel seamless steel pipe or in other similarly harsh conditions. Specifically, a plug for rolling seamless steel pipe in which the surface of a metallic parent material is clad with Co or a Co alloy, and an oxide layer comprising a Co-based oxide is formed on the surface of the clad layer, as well as a method for manufacturing the plug and a method for manufacturing seamless steel pipe in which the plug is used.