A laminated polyester film excellent in blocking resistance and processing suitability and exhibiting excellent electromagnetic transducing characteristics and excellent travel durability, when processed into a magnetic recording medium, and an electromagnetic recording medium using the laminated polyester film as a base film, are provided. This laminated polyester film comprises a polyester layer B containing a cyclic trimer in an amount of not more than 0.8 percent by weight, having a terminal carboxyl group concentration of not more than 35 eq/10⁶ g and containing inactive particles B having an average particle diameter of 50 to 100 nm, and a polyester layer A laminated to one side of the polyester layer B and not containing inactive particles or containing inactive particles A having a smaller average particle diameter than that of the inactive particles B.