This study investigated the effects of chitooligosaccharide on lipid metabolism, immune organ development, and lymphocyte apoptosis in broiler chickens. A total of 480 one-day-old broiler chickens (Arbor Acres) were randomly and evenly assigned to control group and experimental groups I, II, and III. The control group was given a basic diet, while experimental groups I, II, and III were given basic diets for 42 days, supplemented with 50 mg/kg chlortetracycline, 20, and 40 mg/kg chitooligosaccharide, respectively. We found levels of serum triglycerides (TG) and low density lipoprotein cholesterol (LDL-C) to be significantly reduced in experimental group II after 21 days, while the periarterial lymphatic sheath area of the spleens and the average number of bursa of Fabricius nodes were markedly increased. The serum total protein (TP) and high density lipoprotein cholesterol (HDL-C) levels, bursa of Fabricius index, and bursa of Fabricius lobule areas were additionally increased in experimental group III. After 42 days, the serum TP content had also increased and the bursa of Fabricius lobule area was augmented as well in experimental group II. Moreover, the splenic periarterial lymphatic sheat areas and the average numbers of bursa of Fabricius nodes were significantly increased in experimental group III. At both 21 and 42 days, numbers of Caspase 3-positive cells in spleen and bursa of Fabricius were significantly decreased in experimental groups II and III. Our results show that appropriate supplementation of chitooligosaccharide may improve lipid metabolism, promote immune organ development, and inhibit lymphocyte apoptosis in broilers.