Abstract: A resin composition for composite material parts includes a main agent composed of an epoxy resin and a reactive diluent, and a curing agent. The reactive diluent, which is monomer or oligomer of acrylate or methacrylate having one or more vinyl (unsaturated double bond) functional groups and has low viscosity at room temperature, is used in an amount of 5 to 30 parts by weight based on 100 parts by weight of the main agent such that the main agent has a viscosity of 700 to 3000 cps at 25° C. The resin composition of the present invention is very suitable for being used to manufacture composite material parts used in wind blade, boat, automobile and aircraft by the manufacturing process such as vacuum infusion and hand lay-up vacuum assisted resin infusion process.