To provide: a hydroxy group protecting agent which is stable and easy to use, does not have carcinogenicity, a tearing property or the like, and is inexpensive; and a hydroxy group protection method which enables the protection of a hydroxy group under acidic conditions.[Solution] A hydroxy group protecting agent in which at least one protecting group is bound to a nitrogen-containing electron-withdrawing heterocyclic ring through any one of an oxygen atom, a sulfur atom and a nitrogen atom. The heterocyclic ring is a triazine ring or the like, and the protecting group is a benzyl group or the like. Specifically, the hydroxy group protecting agent is 2,4,6-tribenzyloxy-1,3,5-triazine, 2,4,6-tris(4-methoxybenzyloxy)-1,3,5-triazine or the like. In addition, 2,4,6-tris(t-butoxy)-1,3,5-triazine or the like can also be used. For protecting a hydroxy group, a compound of interest which has a hydroxy group is reacted with the hydroxy group protecting agent under acidic conditions.