In order to study the effects of Enteromorpha prolifera on nutrient availability and digestive enzyme activities of broiler chickens, two hundred and forty healthy one-day-old Avian broiler chickens were randomly divided into four groups with six replicates in each group and ten chickens in each replicate. Group Ⅰ (control group) was fed with the diet without Enteromorpha prolifera. Groups Ⅱ, Ⅲ and Ⅳ were fed with the diets with 2%, 3% and 4% Enteromorpha prolifera, respectively, and the nutrient levels of each group were exactly the same except that metabolizable energy was similar. The feeding test lasted for 42 days. At 22 to 28 days of age, apparent nutrient availability of Enteromorpha prolifera and diets were analyzed; and digestive enzyme activities in the gastrointestinal tract of broiler chickens at 42 days of age were measured. The results showed as follows: 1) apparent availability of dry matter, organism matter, and crude protein of Enteromorpha prolifera was 73.90%, 77.53%, and 64.37%, respectively, and apparent metabolizable energy was 8.49 MJ/kg DM; apparent availability of amino acids was 79.10% to 87.59%, and 84.45% on average; 2) compared with the control group, 2% and 3% Enteromorpha prolifera significantly increased the apparent availability of dry matter, energy, organism matter, crude protein and many kinds of amino acids of the diets (P<0.05 or P<0.01); 3% Enteromorpha prolifera had the best effect, and apparent availability of crude protein had the highest improvement among general nutrients; 3) 3% and 4% Enteromorpha prolifera significantly enhanced the activities of pepsin in proventriculus, trypsase in pancreas, duodenum and jejunum, and amylase in pancreas, respectively (P<0.05 or P<0.01); but they had no significant effect on lipase activities (P>0.05). In conclusion, Enteromorpha prolifera has high nutrient availability and rational composition of amino acids, and can increase apparent availability of diets and digestive enzyme activities in the gastrointestinal tract of broiler chickens, so it is an excellent seaweed feed resource. Under this experimental condition, 3% Enteromorpha prolifera has the best effect.［Chinese Journal of Animal Nutrition, 2010，22（6）:1658-1664］