An object is to provide a polyester resin having excellent hydrolysis resistance and good color tone and a method of producing the same. There is provided a polyester resin composition comprising a polyester resin that is prepared from a dicarboxylic acid or a dicarboxylic acid dialkyl ester and a diol as main raw material and mixed with: a copper halide; and at least one additive selected from the group consisting of compounds expressed by a formula (i) and compounds expressed by a formula (ii): MXn . . . (i) (where M denotes an alkali metal or an alkaline earth metal, X denotes at least one element selected from bromine, iodine and chlorine, and n=1 or 2); and (RCOO)nM . . . (ii) (where R denotes hydrogen or an alkyl group containing 1 to 30 carbon atoms, M denotes an alkali metal or an alkaline earth metal, and n=1 or 2).