The adsorption of NO and NO2 on Al2O3(100), SnO2(110) as well as Al2O3(100) supported SnO2 cluster has been investigated using first principle density functional theory calculations. It was found that there is a strong interaction between the SnO2 cluster and the Al2O3(100) surface. The SnO2 cluster dispersed on the Al2O3 surface provides strong binding sites for the NOx adsorption. Compared with Al2O3(100) and SnO2(110) surfaces, both NO and NO2 adsorption and activation are promoted over the Al2O3(100) supported SnO2 cluster.