Abstract: In order to explore the effects of adding chitosan oligosaccharide in the diet on the performance and immune function of broilers, ninety 1-day-old male white-feathered broilers were randomly divided into 5 groups（3 replicates in each group, 6 in each replicate）. Broilers in the control group was fed basal diet. Broilers in the experimental groups Ⅰ, Ⅱ and Ⅲ were fed the basal diet supplemented with 200, 300, 400 mg/kg chitosan oligosaccharide, respectively, and broilers in the experimental group Ⅳ were fed the basal diet supplemented with 200 mg/kg chlortetracycline. The body weight of the chickens were weighed, and feed intake was recorded every day. On the 21 st and 42 nd day of feeding, 3 broilers with similar average body weight were randomly selected from each replicate of each group, and 10 mL of blood was collected from the fin vein to prepare serum, and then the chickens were sacrificed to collect immune organs（thymus, spleen and bursa） and chest muscles. The immune organs were weighed to calculate the immune organ indexes. The contents of immunoglobulin, growth hormone（GH） and insulin-like growth factor Ⅰ（IGF-Ⅰ） were determined by ELISA. After the experiment, the pH value, flesh color and fat content of the muscles in each group were detected. The results showed that compared with the experimental group Ⅳ, the average daily gain of white feather broilers in the experimental group Ⅰ was significantly increased（P＜0.05）, while the feed-to-weight ratio was significantly decreased（P＜0.05）, and the contents of GH and IGF-Ⅰ in serum were also increased. Compared with the control group, the redness（a^*） value of pectoral muscle in the experimental groups Ⅰ and Ⅱ was significantly increased（P＜0.05）, and compared with experimental group Ⅳ, the pectoral muscle yellowness（b^*） value in the experimental groups Ⅰ and Ⅱ was significantly increased（P＜0.05）. Compared with the control group, the bursa index of 42-day-old broilers in the experimental group Ⅲ were significantly increased（P＜0.05）. However, there was no significant difference in thymus index and spleen index compared with the experimental group Ⅳ（P＞0.05）. At the same time, the experimental group Ⅲ could increase the serum IgG content of 21-day-old broilers（P＞0.05）, and significantly increased the serum IgM content of 42-day-old broilers（P＜0.05）, enhanced the immune function of broilers. The results indicated that adding 200 mg/kg chitosan oligosaccharide in the diet could better improve the growth performance and muscle quality of broilers, while adding 400 mg/kg chitosan oligosaccharide could better improve the immune function of broilers, suggesting that chitosan oligosaccharide had the potential as a substitute for antibiotics.