Nano nickel sulfide catalysts (NSCs) were successfully prepared for residue slurry-phase hydrocracking, which were synthesized by precipitation reaction in cetyltrimethylammonium bromide (CTAB) or mixed-surfactant (CTAB and Tween-80)/1-butanol/toluene/water reverse microemulsion in the presence of NiCl2 as the nickel resource and (NH4)(2)S as the sulfiding reagent. The prepared catalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Experimental data revealed that both the kind and content of surfactants play a significant role in the morphology and size of NSCs. The particle size and crystallinity of NSC increased by thermal sulfiding at 300 degrees C in Karamay vacuum gas oil (KLVGO). Optical micrographs showed that NSCs could be well-dispersed in Karamay atmospheric residue (KLAR) without obvious aggregation. On the basis of the lower yields of gas, atmospheric residue (AR), and coke, the NSCs showed higher catalytic activity than a conventional water/oil-soluble Ni catalyst. NSCs had excellent coke suppression performance (coke yield is less than 0.65 wt %), and the produced coke mainly dispersed in liquid products. With the decrease of NSC particle size, the coke suppression performance enhanced and the size of toluene-insoluble fraction in liquid products (TI-LP) decreased. NSCs provided location for coke generation and deposition during the slurry-phase hydrocracking process. The crystal form of NSCs dispersed in the TI-LP was Ni3S2, which was confirmed by XRD analysis.