A six-week experiment was conducted to investigate the effects of supplementing different enzyme cocktails in corn-soybean-byproduct diets on broiler chickens growth performance and nutrient utilization. A total of 630 one-day-old Arbor Acre broiler chicks were randomly allocated to 7 experimental groups with 6 replicates of 15 chicks. The group of chicks serving as the control group were fed a basal diet made of mainly corn and soybean meal, mixed with a little fish meal, rapeseed meal and wheat bran. The other six groups were fed the same basal diet supplemented with each a different enzyme complex at the dosage of 0.75 kg enzyme in 1 t basal diet. At the same time, a metabolic trial was carried out on 42 chicks at the 27 d age. The results showed that the average daily mass gain (ADG) of chicks in the starter phase, age 1 d to 21 d, was improved by all enzyme complex supplements except the cocktail made of 230 IU/g (-amylase, 5.6 kIU/g (-glucanase, 5.3 kIU/g cellulase, 15.5 kIU/g protease and 37.5 kIU/g xylanase. The enzyme cocktail made of 1.6 kIU/g (-amylase, 80 kIU/g protease and 1.6 kIU/g xylanase worked out the most significant difference (P(0.05). Enzyme supplementation decreased the feed conversion ratio (FCR) by 2.78% to 3.98% (P(0.05), indicating better utilization of nutritients. In the grower phase at the age from 22 d to 42 d, the enzyme cocktail made of 4.0 kIU/g (-glucanase, 3.8 kIU/g cellulase, 17.8 kIU/g protease, 4.5 kIU/g xylanase and 44 IU/g (-glactase, and that made of 240 IU/g (-amylase, 1.4.6 kIU/g (-glucanase, 2.0 kIU/g cellulase, 5.7 kIU/g protease, 400 IU/g xylanase, 20 IU/g (-glactase and 200 IU/g phytase imporved chicks ADG and FCR significantly (P(0.05). These two cocktails also were shown to improve ADG and FCR in the entire period of broiler age from 1 d to 42 d. Exogenous digesting enzymes such as protease and amylase benefited the growth and nutrition utilization in young broilers in the starter phase but barely in the grower phase, indicating the underdeveloped intestine of young broilers cannot secrete sufficient digestive enzymes, making an exogenous supplement necessary. Application of an enzyme complex supplement to a maize-soybean diet for broiler chickens challenges attention to selecting suitable enzymes and their proper dosages according to basal diet composition and the age of the broilers.