A polyester resin composition having excellent hydrolysis resistance and excellent transparency and a method of producing the same are provided. There is provided a polyester resin composition comprising a polyester resin that is obtained from a dicarboxylic acid or an ester-forming derivative thereof and a diol as main raw material; and a copper-containing compound and a chelate ligand compound having a nitrogen-containing heterocyclic structure or a tertiary amine structure that are mixed with the polyester resin.