PE and PBT are known to be incompatible polymers. A grafted copolymer PBT-EVA has been generated as a compatibilizer in situ during the processing operation by redistributive transesterification between PBT and EVA in the presence of dibutyl tin oxide (DBTO). This copolymer has been isolated by selective extractions from PBT/EVA/DBTO (49.5/49.5/1% in weight) blend after processing in the melt. It has been evidenced by a H-1-NMR study. This copolymer presents all the resonances of PBT and EVA sequences and some others that have been assigned specificaly to grafting. To achieve these assignments, a model compound obtained by transesterification of EVA with methyl benzoate has been used. When the melt conditions enable synthesis of the grafted copolymer PBT-EVA in situ during processing operations, important changes in the morphology of PE/PBT/EVA/DBTO blends are observed. SEM analysis shows a decrease of PBT particle size and a good adhesion between the PBT and PE phase.