Slurry-phase hydrogenation technology is the frontier topic in the efficient conversion of heavy oils into light fractions around the world.Developing highly active dispersed MoS2 catalysts is the major obstacle to realize the industrial application of upgrading heavy oils.In this work,both top-down ball-milling method and bottom-up hydrothermal method were designed to synthesize MoS2 catalysts with control-lable layer structures.The stacking layers and lateral sizes for micro-scaled MoS2 catalysts by ball-milling method can be reduced to their limits and stabilize at 6 ～ 8 layers and lateral size of ca.30 nm.The more flexible bottom-up hydrothermal method can construct MoS2 catalysts with much smaller lateral sizes and fewer stacking layers,especially,MoS2 catalyst fabricated with ammonium tetrathiomolybdate as Mo and S precursor possesses average stacking layers of 2 and lateral size of 5 ～ 10 nm.polycyclic aro-matic hydrocarbons anthracene,phenanthrene and naphthalene were used as model compounds of heavy oils to investigate the catalytic hydrogenation performance of designed MoS2 catalysts.The cat-alytic activities of MoS2 catalysts can be well correlated with their stacking layers and lateral size.The edges of top and bottom S-Mo-S atomic layers for MoS2 sheets,named rim sites,are positively correlated with the exposure of active sites for catalytic hydrogenation of PAHs.The highest catalytic activity of MoS2 catalyst results from its layer structures of 100％ rim sites and the smallest lateral size of 5 ～ 10 nm,which is beneficial to expose maximum active sites for catalytic hydrogenation reactions.This work can guide us to design the highly active hydrogenation catalysts,and promote the industrial application of upgrading heavy oils.