<p>A polyester film which is useful especially as a base film for magnetic recording media such as a cassette magnetic tape for the digital recording system. The film is produced by irradiating with ultraviolet a surface of a film which is in an unstretched stage or is being stretched to thereby form fine projections on the surface. In the film surface, the ratio of the ten-point average surface roughness Rz to the center-line average surface roughness Ra, Rz/Ra, is lower than 20. The film has a specific value of the ratio of the carboxyl group concentration in a surface part to that in an inner part, and further has the fine projections in a specific number.</p>
