Brinell hardness and tensile strength were measured, weight decrease of specimens due to evaporation of residual monomer were also checked, and the relationship between amount of residual monomer and the mechanical properties were studied. The addition of neopentylglycol dimethacrylate (NPG) in MMA improved the mechanical properties nearly same as the heat processed resins and was effective to decrease residual monomers. Rate of polymerization must increase and the heat of polymerization raised the temperature of curing mass. Properties of the new NPG fluid resin must be improved by loss residual monomer and cross-linking structure.