Abstract: Poly (ethylene terephthalate?butylene adipate) (PBAT) was modified by chain?extension reaction extrusion in a twin?screw extruder using a multi?component epoxy chain extender (ADR), and the effects of the addition amount of ADR on the content of terminal carboxyl groups, relative molecular weight, mechanical properties, crystallinity and color of PBAT were investigated. The results indicated that the terminal carboxyl group content of PBAT was reduced after the chain extension, and its mechanical properties and relative molecular weight were improved. The terminal carboxyl group content of PBAT decreased significantly from 23.3 mol/t to 13.8 mol/t when 1 wt% of ADR was added, and its relative molecular weight, crystallization temperature, and mechanical properties were also improved. Moreover, the maximum mechanical properties were achieved for PBAT when 1 wt% of ADR was added, and its elongation at break was higher than those of the other samples during the aging process. In addition, the PBAT after chain extension exhibited better aging resistance in view of its chemical structure as well as the relative molecular weight higher than the other samples during the aging process.