The effect of hydrotreating of a vacuum gas oil (VGO) feed on the activity, product composition, and quality in a microactivity test (MAT) has been studied. Reduced gas and coke yields and increased gasoline production were observed at constant ASTM conversion after hydrotreating of the VGO feed. Correlations of the activity, gas and coke yield, butene/(total C-4), and (C-1 + C-2)/(C-3 + C-4) ratios are presented as functions of the WC ratio in the feed (degree of hydrogenation) and operation parameters. In the activity correlation a new measure of the degree of cracking is introduced : N-100C = the number of molecules per 100C atoms of the cracking products. The cracking ability increases with increasing hydrotreating. At constant temperature and catalyst/oil ratio the gas yield increases and the coke yield decreases with increasing hydrotreating. Both the (C-1 + C-2)/(C-3 + C-4) and the butenes/(total C-4) ratios are decreasing at increasing H/C ratio and constant operation parameters. The total product value increases as the H/C ratio in the VGO feed increases from 1.56 to 1.73 at constant N-100C.