To provide a novel sealer for a release substrate capable of easily carrying out viscosity adjustment, not exerting a bad influence on curability and adhesiveness of a silicone release agent, and capable of manufacturing a release substrate having a small release load and a small change of the release load over time.

The sealer for the release substrate including 100 pts.wt. of an active energy ray curable resin (a) containing a vinyl group, and 1-60 pts.wt. of water, is used.