NOVELTY - A biaxially-oriented polyester film has a polyester layer (P1) containing polyester (A1) formed using ethylene terephthalate as main structural component, a high-melting point resin (B1) having melting point of 260-320 degrees C, and inorganic particles (C1). The amount of high melting point resin in a layer (P1) is 2-40 %mass. The layer (P1) has dispersed phase consisting of high-melting point resin existing in polyester (A1). The average length of major axis direction of dispersed phase is less than 10000 nm (10 mu m).    USE - Biaxially-oriented polyester film used for solar cell back sheet for solar cell (both claimed). Uses include but are not limited to copper-stuck laminated sheet, adhesive tape, planar heating element, flat cable, capacitor material, motor vehicle material, building material, magnetic recording material, packaging material, photograph material, etc.    ADVANTAGE - The biaxially-oriented polyester film has excellent hydrolysis resistance, ultraviolet resistance and mechanical strength.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) solar cell back sheet (1), which is obtained using biaxially-oriented polyester film; and    (2) manufacture of polyester film. High melting point resin chosen from 1,4-cyclohexane dimethylene terephthalate, ethylene-2,6-naphthalene dicarboxylate and phenylene sulfide, and inorganic particles are melt-kneaded to obtain master pellet. The obtained master pellet and polyester (A1) are melt-kneaded. The melt-kneaded product is extruded in sheet form and biaxially-stretched to obtain biaxially-oriented polyester film. The ratio of melt viscosity (Av) of polyester (A1) at temperature (Tc) ( degrees C) and shear rate of 200 second-1 and melt viscosity (Mv) of master pellet is 0.2-1. The melt-kneading is carried out under condition satisfying relation: Av/Mv greater than or equal to (-0.16x (Tc-Tm)+2.6) and Av/Mv less than or equal to (-0.08x (Tc-Tm)+2.6), where Tm is melting point of high melting point resin and Tc is extrusion temperature ( degrees C) during melting film forming.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic sectional view of solar cell.    Solar cell back sheet (1)    Transparent filler (2)    Electricity generating element (3)    Transparent substrate (4)    Sunlight (5)