PURPOSE: To highly dimensionally reconcile electromagnetic conversion characteristics and a tape edge damage when a polyester film is formed into a magnetic tape by adding particles to the outermost layer at least on a single side and setting the thickness of the outermost layer and the average particle size of the particles to specific relation and setting the Young's modulus of the film in the lateral direction thereof to a specific value.

CONSTITUTION: Particles are added to the outermost layer at least on a single side and the relation between the thickness (t) of the outermost layer and the average particle size (d) of the particles is set to the range of 0.2≤t/d≤5 and the Young's modulus of a film in the lateral direction thereof is set to 600kg/mm2 or more. Polyester films having these characteristics are sufficiently dried to be laminated using two or more extruders, two or more manifolds and a confluent block to form a non-stretched film which is, in turn, biaxially stretched. As preheating and stretching rolls, Teflon or silicone rolls are used in order to improve the surface smoothness of the film. Next, this film is heat- treated.