This study was conducted to evaluate the effects of dietary supplementation with chitooligosaccharide (COS) on growth performance, blood characteristics, relative organ weight, and meat quality in broilers. A total of 480 broilers with an average initial BW of 45.04 g per chick were randomly allocated into 1 of the following 4 dietary treatments (20 broilers per pen with 6 pens per treatment): 1) CON (basal diet), 2) ANT (basal diet + 44 mg/kg of avilamycin), 3) COS0.2 (basal diet + 14 g/kg of COS), 4) COS0.4 (basal diet + 28 g/kg of COS). The experiment lasted for 5 wk and avilamycin was administered from d 0 to 21. Growth performance was measured on d 0, 21, and 35, and all other response criteria were measured on d 35. No change in feed conversion (G:F) was observed in response to any of the treatments throughout the experimental period (P > 0.05). However, BW gain and feed intake were greater (P < 0.05) in broilers provided with feed supplemented with COS than in those in the control group. In addition, broilers had significantly greater (P < 0.05) red blood cell and high-density lipoprotein cholesterol concentrations when they were provided with the COS0.4 diet, whereas the triglyceride concentration was lower (P < 0.05) in broilers in the COS0.2 treatment group. No other blood characteristics were affected by the treatments. Additionally, as the dietary COS concentration increased, the liver weight increased (P < 0.05). Conversely, as the concentrations of dietary COS increased, abdominal fat decreased (P < 0.05). Furthermore, meat yellowness decreased (P < 0.05) as the concentration of COS increased. Finally, the breast meat and abdominal fat of birds provided with feed supplemented with COS had a lower (P < 0.05) saturated fatty acid concentration but a greater concentration of total monounsaturated fatty acids (P < 0.05) than that of birds in the control. In conclusion, COS can improve the performance and breast meat quality of broilers while increasing the red blood cell and high-density lipoprotein cholesterol concentrations in blood. In addition, COS can induce a decrease in abdominal fat and improve meat quality.