The present invention provides a biaxially oriented polyester film for a backsheet of solar batteries which exhibits a good hydrolysis resistance and a low haze. The present invention relates to a biaxially oriented polyester film for a backsheet of solar batteries, comprising titanium in an amount of not more than 20 ppm in terms of a titanium atom, phosphorus in an amount of not more than 70 ppm in terms of a phosphorus atom, and antimony in an amount of not more than 10 ppm in terms of an antimony atom; and having a carboxyl end group content of not more than 26 equivalents/t and an intrinsic viscosity of 0.65 to 0.90.