A method for manufacturing a liquid formulation for reaction injection molding for polymerizing a norbornene-based monomer in the presence of a metathesis polymerization catalyst comprising tungsten as a center metal, the liquid formulation comprising a norbornene-based monomer, provided that in case where the norbornene-based monomer includes exo-dicyclopentadiene, a content of exo-dicyclopentadiene is from 0 to 2% by mass of the norbornene-based monomer, an activator of the catalyst, and a specific ether compound.