To obtain a thermoplastic polyester resin composition capable of providing a molding product excellent in surface appearance without soiling a mold when molding the composition, heightening the crystallization temperature, thereby imparting thermal stability to the molding product without decreasing the transparency, and suppressing the decrease of water vapor permeability, and especially useful for molding of an injection blow molding product.

This thermoplastic polyester resin composition comprises a thermoplastic polyester resin composed of a dicarboxylic acid unit consisting essentially of terephthalic acid or an alkyl ester thereof and a glycol unit consisting essentially of ethylene glycol, obtained by esterification, melt polycondensation in the presence of a polycondensation catalyst, and solid phase polycondensation, and further subjected to an deactivation treatment of the polycondensation catalyst, and an amorphous thermoplastic resin. The content of the amorphous thermoplastic resin is 1 ppb-10,000 ppm.