The study was to investigate the effect of fermented feed on growth, digestion and serum biochemical indexes of Holstein milk bulls. Ten healthy Holstein milk bulls of about 8-month-old [(188.5±29.5) kg] were randomly divided into two groups with five bulls in each group. The control group was fed with basic concentrate, and the experimental group was fed basic concentrate mixed with 20% fermented feed. Corn silage was eaten freely, and each bull in two groups was supplemented with one kg of alfalfa hay per day. The experimental period lasted for 50 days, including five days pre-trial period and 45 days trial period. Average daily gain(ADG), feed to gain ratio(F/G) and economic benefit were calculated during the trial period. Nutrient apparent digestibility was measured by total fecal collection method on the last five days. Blood sample was collected to measure serum biochemical indexes at the last day. The results showed that average daily gain of experimental group was higher than that of control group, but feed to gain ratio was opposite, and the difference was not significant(P>0.05);the apparent digestibility of dry matter and crude protein in experimental group was higher than that of control group(P<0.05), and the apparent digestibility of NDF and ADF was extremely higher than that of control group(P<0.001);the serum total protein, albumin, globulin, urea nitrogen, total cholesterol, triglyceride and low density lipoprotein cholesterol of experimental group were higher than those of control group with significant difference(P<0.05);the gross profit of experimental group was 22.8% higher than that of control group. The experiment indicates that fermented feed can increase average daily gain of dairy bulls, reduce ratio of feed to gain, improve feed utilization efficiency, improve economic benefits and be also conducive to healthy growth of animals.