Abstract: PURPOSE: To obtain a polyolefin resin composition excellent in heat and aging resistances and useful for films for self-adhesive tape substrates of good workability by mixing a base comprising a specified olefin resin with a high-mol. wt. hindered phenol antioxidant and a zinc compound. CONSTITUTION: A resin composition prepared by mixing 100 pts. wt. resin base comprising at least one member selected from among a polyethylene, an ethylene/vinyl acetate copolymer, an ethylene/alkyl acrylate copolymer, an ethylene/alpha-olefin copolymer and a mixture thereof with 0.1-10 pts. wt. high-mol. wt hindered phenol antioxidant and 1-20 pts. wt. zinc compound. Examples of the zinc compound to be used are desirably inorganic compounds and include zinc borate and zinc oxide. As the high-mol. wt. hindered phenol antioxidant, one having a mol. wt. of 500 or above is particularly desirable from the viewpoint of nonblooming properties, etc.