A reinforced polytrimethylene terephthalate resin composition comprising a polytrimethylene terephthalate and an inorganic filler, wherein an amount of the inorganic filler falls within the range from 5 to 70% by weight based on a total weight of the resin composition, an amount of a grafting polytrimethylene terephthalate layer provided on a surface of the inorganic filler falls within the range from 0.1 to 2 parts by weight based on 100 parts by weight of the inorganic filler, and a melt viscosity measured at a resin temperature of 260.degree. C. and a shear rate of 1 rad/sec of a resin component in the resin composition is not more than 600 Pas.