The present application provides a polyester composition composed of polyethylene terephthalate or a polyester containing at least 80 mol % of ethylene terephthalate repeating units and 0.1 to 15 weight %, based on the polyester, of an organic crystallization promoting agent having a polyoxyalkylene chain and at least one epoxy group. The latter promoting agents are represented by such materials as a glycidyl ether of a polyalkylene glycol having a molecular weight less than 5000. Such crystallization promoting agents serve to prevent streaks and pock marks on the surface of articles molded from such polyester compositions.