The present invention relates to a polyester resin. The polyester resin is useful for bottles, sheets, multilayer sheets, stretched films and fiber applications due to excellent heat resistance and transparency, and in particular, the polyester resin has little deterioration of physical properties such as yellowing, etc., during processing. A process for making the polyester resin includes an esterification reaction between a dicarboxylic acid that includes terephthalic acid and a diol that includes isosorbide in the presence of a catalyst, followed by a polycondensation reaction on a product of the esterification reaction. In some embodiments, an initial mixing ratio of the dicarboxylic acid and the diol is between 1:1.02 and 1:1.04.