Provided are a resin composition and masterbatch pellets, which enable a molded resin composition product to improve both flexural modulus and Izod impact strength, and a molded resin composition product having both improved flexural modulus and improved Izod impact strength, and a method for producing the same. The resin composition includes 45 to 95 mass % of an olefin polymer, 1 to 50 mass % of fibrous basic magnesium sulfate, 0.00001 to 0.8 mass % of spherical silica particles, and 0.1 to 10 mass % of a lubricant. Also, the masterbatch pellets are for production of the resin composition by kneading the masterbatch pellets with a diluent containing olefin polymer, and the masterbatch pellets contain 10 to 50 mass % of an olefin polymer, 35 to 80 mass % of fibrous basic magnesium sulfate, 0.00005 to 5.0 mass % of spherical silica particles, and 0.5 to 10 mass % of a lubricant.