A new matrix material for the fluid catalytic cracking (FCC) catalyst was prepared using the zeolite Y mother liquor to modify the surface acidity of γ-Al2O3. The modified γ-Al2O3 was characterized using a variety of techniques, and the relationship between surface acidity and catalytic performances in the catalytic cracking of vacuum gas oil (VGO) was correlated. Characterization results showed that Brönsted acid sites derived mainly from isolated silanol groups, which increased on modified γ-Al2O3, while Lewis acid sites reduced dramatically after modification. Correlation results indicated that increased Brönsted acid sites effectively improved the conversion of VGO. In addition, new medium strong acid sites engendered at the interfaces of γ-Al2O3/amorphous silica-alumina or γ-Al2O3/zeolite Y played a critical role in determining the final product distribution, leading to yields of gasoline and liquefied petroleum gas higher than those of the pure γ-Al2O3 derived catalyst.