Abstract: Beta zeolite is commonly used as an active component in catalyst. The effect of crystal size of Beta zeolite on the hydroupgrading catalyst performance for FCC LCO was studied. Three Ni-Mo catalysts supported on mixture of Al2O3 and Beta zeolites with different crystal size were prepared by impregnation. The catalysts were characterized by XRD and BET methods and evaluated in a micro-reactor using tetralin as a model compound for selective ring opening performance. And a 100mL hydrogenation unit was used for the catalytic performance test using FCC LCO as feedstock. It is found that the catalyst made from smaller crystal size Beta zeolite has higher external surface area and more hydrogenation activity sites, resulting in higher tetralin conversion and better hydroupgrading performance for FCC LCO.