Abstract: A polyester composition includes polybutylene terephthalate and an aliphatic-aromatic copolyester. Based on the total weight of the polybutylene terephthalate and the aliphatic-aromatic copolyester, the content of the polybutylene terephthalate is from 50 to 99% by weight, and the content of the aliphatic-aromatic copolyester is from 1 to 50% by weight. Further, a method for preparing such a polyester composition and a toughened composite material prepared therefrom. The polyester composition has an elongation at break of up to 230% or more, and an improved toughness without substantial loss of strength.