This experiment was conducted to investigate the effects of Enteromorpha prolifera on yolk quality, antioxidant ability and serum biochemical indices of laying hens. Eighty healthy 330-day-old laying hens were randomly divided into 4 groups, and every group had 5 replicates with 4 layers each. Enteromorpha prolifera levels in the diets of four groups were 0 (control group), 2% (group Ⅰ), 3%(group Ⅱ), 4%(group Ⅲ), respectively. The experiment lasted for 49 days. The results showed as follows: compared with the control group, 4% Enteromorpha prolifera could significantly increase the yolk color (P<0.05), phospholipids (P<0.05), crude protein (P<0.05), ferrum (P<0.01)and iodine (P<0.01) contents in yolk, and the contents of potassium (P<0.01), total protein (P<0.01) and albumin(P<0.01) in serum, enhance the superoxide dismutase activity in serum (P<0.05), decrease the content of cholesterol (P<0.01) in yolk, total cholesterol (P<0.05) and triglycercide (P<0.05) in serum, and the glutamic-pyruvic transaminase activity (P<0.01) in serum. In conclusion, Enteromorpha prolifera can enhance the yolk quality and antioxidant ability, improve the minerals, lipid and protein metabolism of laying hens. It can be appropriate used with a level of 4% in production.［Chinese Journal of Animal Nutrition，2011，23（3）：452-458］