This experiment was conducted to evaluate the effects of dietary digestible sulphur amino acids (DSAAs) level on growth performance, blood metabolites, and liver functional enzymes of broilers during 1-11 days of age. Additionally, DSAAs requirement was determined from dose nutrient response data. A total of 432 one‐day‐old male Ross 308 broilers were allocated to six dietary treatments, graded levels of supplementary DL-Met (+0.8 g/kg per level) while Cys was equal across groups, led to levels of 0.62%, 0.70%, 0.78%, 0.86%, 0.94% and 10.2% DSAAs, with six replicates and 12 birds each. Increasing levels of dietary DSAAs enhanced live body weight (LBW), weight gain (WG), feed efficiency (FE), European Production Efficiency Factor (EPEF), and relative breast weight (RBW), although there was no effect on feed intake. At the end of the starter period, a linear increase in blood serum total protein and albumin concentration was concomitant with decreasing in triglyceride, whole cholesterol, high‐density lipoprotein, low‐density lipoprotein, creatinine, and aspartate aminotransferase concentration when dietary DSAAs level was increased. The DSAAs requirements estimated by linear broken-line (LBL) fit model to optimize LBW, WG, FE, EPEF and RBW were 0.80%, 0.81%, 0.93%, 0.95% and 0.93%, although the estimated values by the quadratic broken line fit model were 14.32%, 19.93%, 16.85%, 23.68% and 5.79% higher than those, respectively. It is concluded, a minimum of 0.95% DSAAs concentration in broiler starter diet is suggested to optimize growth performance. Estimation of DSAAs requirement depended on what production parameter and regression model are taken considered for optimization.

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