Chitosan oligosaccharide (COS) and valine (Val) supplementation will improve growth performance, carcass traits, hormonal profile and meat quality in broilers. To evaluate this hypothesis, based on a 2×4 factorial arrangement, 480 male broilers (Ross 708) were randomly placed in eight treatment groups for two levels of COS (C1: 100 mg/kg, and C2: 150 mg/kg) and four levels of valine (V1: 0.57%, V2: 0.72%, V3: 0.87% and V4: 1.02%) with three replicates (n=24) with 20 birds in each (ni=60; i=1, 2, 3,…, 8.). The results showed that live bodyweight (BW), weight gain (WG), and carcass weight increased, and feed conversion ratio (FCR) decreased with increased supplemental levels of dietary Val at C1 and C2. Abdominal fat reduced linearly for both COS and Val, with a higher reduction response value at C2 and V4. The serum levels of triiodothyronine (T3), thyroxine (T4), testosterone and insulin-like growth factor 1 (IGF-1) presented a linear effect for COS and Val. The proximate composition of breast and leg meat showed that crude fat content decreased linearly for COS and Val with higher reduction response values at V3 for both levels of COS. The ash content rose linearly with increasing concentration of Val at C1, but showed the highest value at V2 when birds were offered C2. There was an interaction between COS and Val for T3, T4, IGF-1, ash content and crude fat. In conclusion, supplementation exerted a significant influence on the growth performance, hormonal profile and meat composition of broilers.