Production method for stabilized olefin resin composition

Provided is a production method capable of imparting a sufficient stabilization effect on an olefin resin composition and thereby producing an olefin resin composition having superior long-term stability. This method for producing an olefin resin composition containing a polyolefin resin obtained through polymerization by adding, to a catalyst system or a polymerization system before or during polymerization of an olefin monomer, a mixture obtained by mixing a phenolic antioxidant represented by general formula (1) and a phosphite compound represented by general formula (2) or general formula (3) with an organic aluminum compound or a mixture solvent of an organic aluminum compound and an organic solvent. With respect to 100 parts by mass of the olefin resin obtained through polymerization, the contained amount of the phenolic antioxidant represented by general formula (1) is 0.001-5 parts by mass and the contained amount of the phosphite compound represented by general formula (2) or general formula (3) is 0