A series of mesoporous ZSM-5-x (x = Si/Al molar ratio) supports, possessing various Si/Al ratios, were prepared without using the secondary templates, and the influences of acidity of ZSM-5-x on catalytic performance of Pt/HZSM-5-x samples prepared by the conventional wetness impregnation in naphthalene hydrogenation were investigated. The results show that decreasing Si/Al ratios of mesoporous ZSM-5 supports promotes the dispersion of the supported Pt species, and the catalytic efficiencies of Pt/HZSM-5-x samples for naphthalene hydrogenation depend on the integrated effects of the Pt dispersion, the acidity, and the mesoporous structure of ZSM-5 supports. This work provides the detailed influences of acidity of mesoporous ZSM-5 on catalytic performance of supported Pt catalysts in naphthalene hydrogenation.