This study concerns the reactive compatibilization of the blend of poly(butylene terephthalate) (PBT) and ethylene/vinyl acetate copolymer (EVA) by maleic anhydride (MAH). First, the graft copolymerization of EVA with MAH was investigated using dicumyl peroxide (DCP) as an initiator by melt free radical grafting in a plasticorder (Haake). The concentrations of MAH and DCP were varied from 0 to 3.0 phr and from 0 to 0.4 phr, respectively. EVA-g-MAH formed by the grafting reaction of EVA and MAH in the presence of DCP exhibits a significantly lower torque value than EVA bearing no MAH. PET was blended with thus-obtained EVA-g-MAH using the same plasticorder. For comparison, PBT/EVA blend was also prepared. The FTIR spectroscopic studies showed that PBT-g-EVA copolymer was formed by the in situ interfacial reaction of MAH grafted onto EVA with the carboxylic and/or hydroxyl groups at the chain ends of PET in the blend systems. The impact strength of PBT/EVA-g-MAH (80/20) blend showed about three-fold increase in comparison with PBT/EVA (80/20) blend due to the enhanced interfacial adhesion by the formation of in situ compatibilizer, i.e. PBT-g-EVA copolymer. Also, the morphology of the blends was observed with scanning electron microscope (SEM). (C) 2001 Published by Elsevier Science Ltd.