Abstract: A method for the production of polyester film is disclosed including the steps of: esterifying at least one species of carboxylic acid with at least one species of glycol; adding to the ester composition macro particles of silica of an average diameter of approximately 1.3 to approximately 2.0 .mu.m and fine particles of aluminum oxide of an average diameter of approximately 20 to approximately 200 nm; polycondensing the resulting mixture, to give a filled polyester resin; melting the filled polyester resin; molding the melt into a sheet; and biaxially stretching the sheet to produce a film product which is superior in haze and in static friction coefficient (U.sub.x)/kinetic friction coefficient (U.sub.k) ratio The polyester film of the present invention does not appear milky. In addition, after slitting the polyester film and tightly winding it around a roll it does not have a substantial number of protrusions.

Abstract: A method for the production of biaxially stretched polyester film.The method comprises the steps of: adding cubic calcium carbonate particles of calcite structure satisfying the following conditions at any stage of polyester preparation, so as to prepare polyester resin:d.sub.25 /d.sub.75 <2.00 (1)0.7.ltoreq.d.sub.50 .ltoreq.1.50 (2)a:b:c=1:(1.about.1.5):(1.about.1.5) (3)wherein d.sub.25, d.sub.50 and d.sub.75 are the diameters (.mu.m) of particles when the accumulated weights of the particles are on the order of 25, 50 and 75% of the total weight of the particles, respectively, and a, b, c are width, length and height of the cubic calcium carbonate particles and the shortest one among a, b and c is set a=1; and applying melt-extrusion to the polyester resin.The biaxially stretched copolyester film provided is superior in travelling capacity as well as abrasion resistance and scratch resistance, so that it is useful for magnetic recording media.