The present invention provides a method of producing an olefin resin composition by which an olefin resin composition in which reduction in the physical properties and occurrence of yellowing after a sterilization treatment by irradiation with radiation are suppressed can be produced.The method of producing an olefin resin composition according to the present invention is a method of producing an olefin resin composition for a molded article to be used after a sterilization treatment by irradiation with radiation, the method comprising: blending, before or during polymerization of an olefin monomer, a phenolic antioxidant, which is represented by the following Formula (1) and masked with an organoaluminum compound, in an amount of 0.001 to 0.5 parts by mass with respect to 100 parts by mass of an olefin resin obtained by the polymerization; and blending, at any one point of before, during or after the polymerization of the olefin monomer, a phosphorus-based antioxidant in an amount of 0.001 to 3 parts by mass with respect to 100 parts by mass of the olefin resin obtained by the polymerization: (wherein, R represents, for example, an alkyl group having 12 to 24 carbon atoms which is optionally branched and/or substituted).