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• ASA with the different Al/Si ratio were synthesized by a simple co-precipitation method. • The Al/Si ratio affects the Al coordination state, pore structure, acidity and surface properties of ASA. • Mo/ASA-4 with the largest amount of Mo atoms located at edge sites can provide the most amount of exposure Mo active sites. • Mo/ASA-4 catalyst achieves the highest yield of value light oil and the lowest yield of gas and coke due to its excellent hydrogenation activity. To deeply illuminate the effect of ASA composition on its corresponding Mo catalyst properties and performance for the slurry-phase hydrocracking of vacuum residue, the amorphous silica-alumina (ASA) samples with the various ratios of Al to Si were successfully synthesized by a simple co-precipitation method, which have the different acid properties and pore structure, especially ASA-1 with lowest ratio of Al to Si owning the largest number of B acid sites and the highest volume of mesoporous. Additionally, the Mo catalyst supported on ASA-4 possesses the highest dispersion of MoS 2 slabs and largest amount of Mo atoms located at the edge sites among all the catalyst, possibly due to the appropriate surface properties of ASA-4 derived from the ratio of Al to Si, it demonstrates that the most exposure Mo active sites are present on Mo/ASA-4 catalyst. The hydrocracking evaluation results show that the VR conversion over the different catalysts are similar, it may be ascribed to the variation of acid properties and pore structure insufficient to change VR cracking pathway because of the low catalyst dosage. Furthermore, the Mo/ASA-4 catalyst exhibits the higher yield of naphtha and middle distillate and inversely the lower yield of gas and coke in comparison with other catalysts, it should be attributed that the higher hydrogenation activity derived from the more exposure Mo active sites can efficiently restrain the over-cracking of the intermediate product and aggregation of the polycyclic aromatic hydrocarbon in the hydrocracking process. [ABSTRACT FROM AUTHOR]