This study was conducted to determine the effects of supplementing threonine (Thr) at different levels in the diets on growth performance and immune responses of broiler chickens challenged with infectious bursal disease (IBD) and also to estimate Thr requirement based on different response criterion. A total of 300 one-day-old male broiler chicks were assigned to one of the six dietary treatments. Chickens were fed eight graded levels of Thr: 0.60, 0.67, 0.74, 0.81, 0.88 or 0.95% from day 21 to 42 of age. On day 28, all birds were challenged with a commercial live-IBDV vaccine. Body weight gain (BWG), feed conversion ratio (FCR) and carcass characterisation (breast, thigh and fat pad percentage) were significantly influenced by Thr levels. Increasing advisable level up to 0.81% of the diet resulted in significant improvement in the FCR and BWG. Thr supplementation had great effects on the antibody titer against IBD; the broilers receiving the Thr levels of higher than National Research Council (NRC) recommendation have a higher IBD antibody titer than those that received lower levels of Thr. The highest (0.822490.0211) and the lowest (0.724090.0140) were estimated with straight broken-line analysis for immune response (14 days post-challenge) and breast weight, respectively. The results obtained in the present study indicated that Thr requirements of broiler based on the recommendation of NRC are not sufficient to meet the requirement of the new commercial broiler companies under stress and non-hygienic conditions. The best level of Thr based on the current study was 0.81% for support growth performance and immune function.