NOVELTY - A polyester film comprises first resin layer and second resin layer which contain polyester and titanium compound derived from catalyst in which fusion lamination of first resin layer is carried out at single side of second resin layer. The temperature rising crystallization peak (Tc1) of first resin layer at time of measuring with temperature increase rate of 5 degrees C/minute with differential scanning calorimeter is 130-160 degrees C when IV1 (dl/g) and terminal carboxyl group density are set to AV1 (equivalent/ton) of less than or equal to 20 and degree of plane orientation is set to 0.14-0.2.    USE - Polyester film for solar cell backside sealing, solar cell back surface protective film and solar cell module (claimed).    ADVANTAGE - The polyester film has hydrolysis resistance and high withstand voltage property.    DETAILED DESCRIPTION - A polyester film comprises first resin layer and second resin layer which contain polyester and titanium compound derived from catalyst in which fusion lamination of first resin layer is carried out at single side of second resin layer. The temperature rising crystallization peak (Tc1) of first resin layer at time of measuring with temperature increase rate of 5 degrees C/minute with differential scanning calorimeter is 130-160 degrees C when IV1 (dl/g) and terminal carboxyl group density are set to AV1 (equivalent/ton) of less than or equal to 20 and degree of plane orientation is set to 0.14-0.2. The second resin layer has temperature rising crystallization peak of 150-180 degrees C at time of measuring with temperature increase rate of 5 degrees C/minute with differential scanning calorimeter (DSC), degree of plane orientation of 0.12-0.18. The relationship of glass transition temperature of first resin layer and glass transition temperature of second resin layer is 5-0.5. INDEPENDENT CLAIMS are included for:    (1) manufacture of polyester film involving co-extruding second fusion membranous substance for forming first fusion membranous substance and second resin layer for forming first resin layer using resin composition containing polyester and titanium compound derived from catalyst, co-extrusion process of forming laminated body in single side of second fusion membranous substance by carrying out fusion lamination of first fusion membranous substance, performing longitudinal stretch and lateral stretch of laminated body, extending process, heat-setting process of biaxially stretched film, and heat-setting process;    (2) solar cell back surface protective film comprising polyester film; and    (3) solar cell module comprising polyester film.