The present invention provides a both surfaces-laminated polyester film having a coating layer excellent in easy adhesion property to a hard coat layer and another coating layer having an ability of preventing precipitation of oligomer.A both surfaces-laminated polyester film comprising: a polyester film, a first coating layer which is formed on one surface of said polyester film and comprises a polymer containing ammonium base, an acrylate polymer containing polyethylene glycol and a crosslinking agent, and a second coating layer which is formed on another surface of said polyester film and comprises a polyurethane resin and a crosslinking agent.