The polyester composition for films includes, based on 100 parts by weight of a polyester resin, 0.01 to 5 parts by weight of aluminum silicate particles containing aluminum and silica as principal components and an alkali metal. To provide polyester films suitable for magnetic recording media, the polymer composition contains surface- modified aluminum silicate particles and two additional particles distinct in particle diameter. The polyester films thus obtained have excellent abrasion resistance and scratch resistance.