Chitosan oligosaccharides (COs) have varying physiologic activities. This work aims to explore effects of dietaryCOs on the laying performance, egg quality, and plasmabiochemical indicators of laying ducks.Four diets were formulated by supplementing different dosages (0, 25, 50, and 100 mg/kg) of COs in basal diet. A total of 288 Suyou No.2 healthy laying ducks at peak egg production stage with age of 28 weeks, similar weights (1500 ± 106 g) and egg laying rates were randomly evenly assigned to four groups, with 6 replicates in each group. Dietary 50 mg/kg of COs increaseddaily egg production (EP), egg mass (EM), egg weight (EW), eggshell strength,yolk color, serumsuperoxide dismutase (SOD) and glutathione peroxidase (GPX) activities, and immunoglobulin (Ig) G, Ig A, Ig M, and high-density lipoprotein levels (HDL-C). Conversely, itdecreased the feed conversion ratio (FCR), yolk percentage, and serum malondialdehyde (MDA), total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol (LDL-C) levels of laying ducks. Nevertheless, a high dosage of COs (100 mg/kg) neither decreased nor improved the efficiency. The optimum dose of COssupplementation required for the maximum egg mass of laying ducks was 61.41mg/kg.These results indicated that COs supplementation at an appropriate dosage could ameliorate the laying performance, egg quality, and health condition of laying ducks.