Abstract: By a conventional preparation method of thick film gas sensor,pure ZnO thick film sensors and two Al₂O₃-doped（the contents of Al₂O₃ are 2wt% and 5wt% respectively） ZnO thick film sensors were fabricated from ZnO（with average particle size of 30 nm） and Al₂O₃ nanoparticles（the average particle size was 5 nm）.The intrinsic resistances and gas sensing performance of the samples to ethanol vapor were tested.The results indicate that the intrinsic resistances and the working temperatures of ZnO gas sensors decrease with the doping of Al₂O₃.At the same time,the sintering properties and the sensitivities of these gas sensors are improved.Furthermore,the reason for the above improvement is analyzed on the basis of morphology observation of these thick film sensors.