To provide a polyester resin composition excellent in a gas barrier property and flexibility without impairing a hue.

The polyester resin composition comprises a polyester resin, a germanium compound and a phosphorous compound. In the resin composition, total content of the germanium compound and the phosphorus compound is 10-2,000 ppm and the molar ratio of a germanium element to a phosphorus element is (20:1) to (1:5) and the contents of one or more transition metals selected from manganese, titanium, antimony, tin, cobalt and chromium are not each ≥5 ppm. The polyester resin composition excellent in the gas barrier property and the flexibility can be obtained without impairing the hue by using such the polyester resin composition. The polyester resin composition is used for application such as bottles.