We demonstrate that the single-site catalyst Pt1/CeO2 greatly enhances the selectivity of cyclization and aromatization in the n-hexane reforming reaction. Specifically, the selectivity of single-site Pt1/CeO2 toward both cyclization and aromatization is above 86% at 350 °C. The turnover frequency of Pt1/CeO2 is 58.8 h-1 at 400 °C, which is close to that of Pt cluster/CeO2 (61.4 h-1) and much higher than that of Pt nanoparticle/CeO2 with Pt sizes of 2.5 and 7 nm. On the basis of the catalytic results for methylcyclopentane reforming, the dehydrocyclization and further aromatization of n-hexane are attributed to the prominent adsorption of ring intermediate products on the single-site Pt1/CeO2 catalysts. On the other side, with the multiple Pt adjacent active sites, the cluster and nanoparticle Pt/CeO2 samples favor the C-C bond cracking reaction. Ultimately, this in-depth study unravels the principles of hydrocarbon activation with different Pt sizes and represents a key step toward the rational design of new heterogeneous catalysts.