Alkylating benzene with ethane is advantageous but more challenging than the conventional alkylation with ethylene. The present work explored rational design of Pt/ZSM-5 bifunctional catalysts for alkylating benzene with ethane to produce ethylbenzene. Here, two series of ZSM-5 nanosheets with different b-axis thicknesses (30 ∼ 400 nm) and varied Si/Al ratio (10 ∼ 100) were synthesized for preparing Pt/ZSM-5 catalysts. The catalytic performance (conversion of ethane and benzene, EB selectivity) of these catalysts was evaluated in direct alkylation of benzene with ethane. As expected, Pt/ZSM-5 with smallest average nanosheet thickness delivers the highest ethylbenzene yield (the yield with 30 nm nanosheet is ∼1.5 times that with 400 nm nanosheet), attributed to its high accessibility to acid sites and favourable diffusion condition. Most significantly, this study reveals that the Si/Al ratio of ZSM-5 regulates the dispersion and particle size of Pt of Pt/ZSM-5. With same Pt loading, the Pt/ZSM-5 catalyst with a lower Si/Al ratio exhibits a higher Pt dispersion and smaller particle size. This is attributed to the interaction between H+ of ZSM-5 and Pt. The interaction not only has the anchoring effect for Pt (thus enhances the Pt dispersion on ZSM-5 and limits the Pt particle size), but also weakens the acid strength. These two effects work interactively in controlling the product distribution and accompanied side reactions in alkylation of benzene with ethane. When optimized, at ultralow Pt loading of 0.05 wt%, Si/Al of 30 and ZSM-5 nanosheet thickness of 30 nm, the Pt/ZSM-5 catalyst delivers high ethylbenzene selectivity and yield with stability and completely suppresses the methane selectivity.