A biaxially oriented polyester film formed from an aromatic polyester composition containing:(A) 100 parts by weight of an aromatic polyester, and(B) 0.005 to 5 parts by weight of calcium carbonate particles defined by:(a) a length/width ratio (2a/2b) in the range of from 1.25 to 3,(b) an average particle diameter (D), as a diameter of a circle converted from an area, in the range of from 0.05 to 5 .mu.m, and(c) an ellipse coefficient, represented by the following equation (1), in the range of from 0.7 to 1.2, ##EQU1## wherein R is an ellipse coefficient, S.sub.1 is an observed area of a projected plane of a particle, and S.sub.2 is an elliptical area determined on the basis of observed values of the length (2a) and width (2b);and a magnetic recording medium formed of the above biaxially oriented polyester film and a magnetic layer formed thereon.