The effect of zeolite beta particle size on the HDS, HDN, and HDA activities of LCO hydrotreating was investigated on Mo-Ni and W-Ni supported on nano- and micro-sized zeolite beta hydrotreating catalysts. The catalysts were characterized by XRD, BET, TEM, and XPS, and evaluated with an autoclave using real LCO as feed. It was concluded that, with the Mo-Ni catalysts, the catalyst containing nano-sized zeolite beta particles had similar hydrogenation activity as the one containing micro-sized (conventional) particles; with the W-Ni catalyst, the nano-sized zeolite catalyst presented higher HDS, HDN, and HDA activities as expected. Higher liquid yields Could be achieved by using the W-Ni and Mo-Ni nano-sized zeolite catalysts. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.