In the present invention, a masterbatch is produced by melt-mixing a metal compound (B) with a reactive thermoplastic resin (C). The oxidizable polyamide (A) is produced by polycondensing a diamine component containing m-xylylenediamine in an amount of 70 mol % or higher with a dicarboxylic acid component containing adipic acid in an amount of 50 mol % or higher. The metal compound (B) contains at least one metal selected from the group consisting of transition metals in group VIII of the periodic table, manganese, copper and zinc. The reactive thermoplastic resin (C) has an internal bond and/or a reactive functional group which are reactive with an amide bond and/or a reactive functional group of the oxidizable polyamide (A). The masterbatch exhibits a stable moldability. The masterbatch is melt-mixed with an oxidizable polyamide (A) and formed into a molded article which exhibits an excellent oxygen-absorbing ability irrespective of the preservation conditions of the masterbatch.