To provide a mixture solution containing a norbornene monomer for reaction injection molding for obtaining a molded item with few sink marks notwithstanding shapes or sizes of a mold, or shapes, sizes or thickness of the molded item, or the like, a manufacturing method of an injection-molded item using the mixture solution, and an injection-molded item obtained by the same.

The mixture solution for reaction injection molding by causing a norbornene monomer to bulk polymerize in a mold comprises the norbornene monomer, a polymerization catalyst and an elastomer having a shear rate coefficient of at least 1.30 and at most 1.60. The manufacturing method of the reaction injection-molded item comprises using the mixture solution. The reaction injection-molded item is obtained by the manufacturing method.