To provide films having uniform surfaces, excellent in traveling properties, abrasion resistance and clarity and applicable to various uses such as graphic arts, displays, packaging, transfer marks, magnetic recording media and electrical parts such as condensers.

Desired biaxially oriented films are obtained by biaxially orienting a polyester containing 0.001-3.0 wt.% porous spherical silica particles having an average particle diameter of 0.3-15 μm, a spherical ratio, defined by equation I: spherical ratio = projected area of particle/area corresponding to circle of maximum diameter at projected plane of particle, of 0.90-1.0 and a particle size distribution value, defined by equation II: particle size distribution value = d10/d90 (wherein d10 and d90 are particle diameters (μm) corresponding to 10% and 90% of the entire volume of particles by measuring the integrated volume of particle groups from the side of greater particles, respectively, of 1.2-2.5, and the degree of deformation of the porous spherical silica particle is 1.2-5.0.