A polypropylene resin composition comprising (A) 99.8 to 80 weight parts of a polypropylene resin having a melt flow rate of 0.1 to 50 g/10 min and (B) 0.2 to 20 weight parts of an olefin copolymer rubber having an intrinsic viscosity [.eta.] of 0.5 to 4.0 dl/g and/or a polyethylene resin having a density of 0.895 to 0.945 g/cc and a melt flow rate of 0.05 to 15 g/10 min, which have undergone an ionization ray-irradiation treatment and/or a treatment of adding 0.05 to 5 weight parts of an organic peroxide to 100 weight parts of the aforesaid polypropylene resin composition comprising (A) and (B) and then melting.