The present invention relates to a polyester resin including a diol constitutional unit and a dicarboxylic acid constitutional unit as main constitutional units, in which the diol constitutional unit contains from 70 to 95% by mol of a constitutional unit derived from ethylene glycol and from 5 to 30% by mol of a constitutional unit derived from tricyclodecane dimethanol or pentacyclopentadecane dimethanol, and the dicarboxylic acid constitutional unit contains 50% by mol or more of a constitutional unit derived from a naphthalenedicarboxylic acid, and an optical lens obtained by molding the polyester resin. According to the present invention, there are provided a polyester resin that has a high refractive index and a low Abbe number and can be molded into a good optical lens, and an optical lens obtained by molding the polyester resin.