Abstract: Two Al₂O₃ supports were characterized by means of NH₃-TPD, FT-IR and N₂ adsorption-desorption. The characterization results showed that the two Al₂O₃ supports have no significant differences in their total acidity and acidity strength. The acid sites are mainly Lewis ones, but Al₂O₃ (b) has larger average pore diameter and pore volume than Al₂O₃ (a). The influence of the pore structures of the Al₂O₃ supports on the full range FCC gasoline upgrading performance of the nanosized HZSM-5 based catalysts was investigated in a fixed-bed reactor. The results indicated that the HZSM-5 catalyst extruded with macroporous Al₂O₃ exhibited superior activity, stability and performance in reducing olefin content of FCC gasoline. The modified nanosized LaNiMo/HZSM-5 catalyst reduced olefin and sulfur concentration in FCC gasoline by about 83% and 87% within 300 h time on stream, respectively, meanwhile the gasoline octane number was preserved.