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 gamma-Al2O3. The modified gamma-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 Bronsted acid sites derived mainly from isolated silanol groups, which increased on modified gamma-Al2O3, while Lewis acid sites reduced dramatically after modification. Correlation results indicated that increased Bronsted acid sites effectively improved the conversion of VGO. In addition, new medium strong acid sites engendered at the interfaces of gamma-Al2O3/amorphous silica alumina or gamma-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 gamma-Al2O3 derived catalyst.