ABSTRACTThe digestible lysine requirement for the growth performance of broilers fed diets with decreasing energy to protein ratio and reared under subtropical summer conditions were determined. Treatments consisted of five wheat-based diets with five levels (0.90, 0.95, 1.00, 1.05 and 1.10%) of digestible lysine (DL) and lowering energy to protein ratio (EPR; 13.6, 12.8, 12.0, 11.4 and 11.0), with five replicates of 80 birds each (n = 2000). Body weight gain (BWG) significantly increased by increasing DL levels during wk 1 (p<0.001), while 1.05% DL promoted the highest BWG during the whole experimental period (p<0.01). Increasing DL level resulted in significant reduction in feed intake (FI) and BWG to DL intake ratio (BWG:DLI) during wk 1-3 (p<0.05). Feed:gain ratio (FGR) significantly (p<0.01) improved with DL levels up to 1.05% during the whole experimental period, except for wk 5. The increasing ambient temperature had a linear effect on the all growth parameters. It is inferred that best growth performance can be obtained at 1.05% DL, maintaining all other AA constant under subtropical summer conditions.