A method for the production of polyester suitable to be molded into a film with excellent surface properties.The method comprises passing dispersion-in-water type silica sol with pH 8 to 11 including sodium oxide as a stabilizer and silica particles with average diameters 0.01 to 0.3 .mu.m through a column of cation exchange resin having the following formula 1 and the strong basic anion exchange having the following formula 2, in sequence to adjust the pH value to 2 to 4, adding an hydrogen bonding agent and ethylene glycol thereto, heating the resultant silica sol under a reduced pressure to remove water, so as to obtain dispersion-in-ethylene glycol type silica sol, and adding 0.01 to 5% by weight of the dispersion-in-ethylene glycol type silica sol, as based on the weight of polyester to be produced, at any step during the ester interchange reaction. ##STR1##