To provide a polyester film for a light diffusing film having excellent thermal stability and no warpage which can be used as the base material for a light diffusing film having sufficient adhesion strength of the film with the light diffusing layer.

The polyester film for a light diffusing film has ≥80% transmittance for whole rays and ≤10×10-6/°C coefficient of thermal expansion and has the following coating layer on at least one surface. The coating layer is formed from a coating liquid containing at least one kind of compound selected from a polyester resin, acrylic resin, polyurethane resin, amino resin, epoxy resin, oxazoline resin and coupling agent.