A total of 192 Noi broilers at 56 days of age were allotted in a completely randomized design consisting of four treatments and four replicates to evaluate the effect of dietary lysine added on body weight gain (BWG), feed conversion ratio (FCR), apparent nutrient digestibility (AND), and carcass characteristics. Treatments included a control with 0.8% lysine in the diet and three experimental treatments (Lys+0.1; Lys+0.2; Lys+0.3) with lysine added at 0.1, 0.2, and 0.3%, respectively. Crude protein (CP) was 15%, and metabolizable energy was 3,000 kcal/kg of feed. At 77 days of age, for each replicate, one male and one female chicken were selected for the estimation of AND by using Fe2O3 marker. The chickens were fed ad libitum and vaccinated against common diseases. The results showed that lysine's addition to the diet at 0.2–0.3% significantly improved the BWG and FCR (P

Key words: Digestibility, Lysine, Noi broilers