A release-treated substrate is a release-treated substrate having a release treating agent layer by a cationically polymerizable ultraviolet curing silicone treating agent at least partially on at least one side of the substrate, and is characterized in that the cationically polymerizable ultraviolet curing silicone treating agent is at least partially applied to at least one side of the substrate, and heat treatment is then conducted before conducting ultraviolet irradiation treatment. As the cationically polymerizable ultraviolet curing silicone treating agent, a cationically polymerizable ultraviolet curing silicone treating agent in which a modified silicone polymer component having at least two epoxy groups in the molecule is an effective component is suitable. It is preferable that temperature in the heat treatment is from 35 to 120.degree. C.