In the production of glycidyl methacrylate from an alkali metal salt of methacrylic acid and epichlorohydrin, at least one water-soluble polymerization inhibitor is added at an appropriate stage of the production. The addition of the water-soluble polymerization inhibitor prevents the formation of insoluble solid matters to increase the efficiency of phase separation in the washing operation for removing a by-produced salt and form a clear interface between the phases, thereby minimizing the recovery loss. In addition, the troubles such as clogging of pipe lines of production apparatus and equipment for waster water treatment can be avoided.