This study was conducted to investigate effects of supplementation with a chito-oligosaccharide (COS) on growth performance, nutrient digestibility, blood characteristics and diarrhea incidence in weanling pigs. A total of 120 Landrace×Yorkshire–Duroc pigs (21±1d of age) with an average initial BW of 7.10±0.48kg were randomly allotted to four dietary treatments, with six pens per treatment and five pigs per pen. A maize–soybean meal-based diet was formulated as a basal diet. Experimental treatments included: 1) CON, basal diet; 2) ANT: basal diet+antibiotics (phase 1, 40mg/kg avilamycin and 100mg/kg oxytetracycline; phase 2 and phase 3, 40mg/kg chlortetracyclinean and 100mg/kg neomycin); 3) COS1, basal diet+1g/kg COS; and 4) COS2, basal diet+2g/kg COS. The experiment consisted of three phases (d 0 to d 7, d 8 to d 21 and d 22 to d 42) and lasted 42d. Improved growth performance and total tract apparent digestibility (TTAD) of dry matter (DM) and nitrogen (N) only applied to the high inclusion level of COS (2g/kg) (P<0.05) and both performance and digestibility were lower (P<0.05) than for the group supplemented with antibiotics. However, lymphocyte concentration and appearance of the diarrhea decreased (P<0.05) in response to supplementation of COS. The results of the current study indicated that dietary supplementation with 2g/kg COS enhanced growth performance and improve TTAD of DM and N.