This study was conducted to evaluate the effect of dietary protein level and amino acid supplementation on tilapia nursering performance under biofloc system conditions at cold suboptimum temperature. Four experimental diets were organized; 30% CP diet as positive control (30P), 22% CP diet as negative control (22P), 22% CP diet supplemented with 1% lysine (22PL) and 22% CP diet supplemented with 0.5% threonine (22PT). Formulated diets were tested under biofloc system conditions in three replicates for each treatment. 12 experimental tanks (1000L) were used, each of which was filled with 400 L and stocked with 50 fries (6.20±0.01 gm/fish). The experiment extended for 97 days. Results revealed that fish fed on 22PT diet recorded the highest significant values of weight gain (WG), feed intake (FI), feed conversion ratio (FCR) and specific growth rate (SGR) (11.10, 16.95, 1.55 and 1.40, respectively). Additionally, the 22PT diet groups recorded the highest protein content of dried microbial floc and wet whole-body. While the lowest total ammonia nitrite (TAN) values were recorded for the fish groups fed on 22PT diet. Thus, under biofloc system conditions, a low protein diet supplemented with threonine can improve biofloc system performance during the tilapia nursering in cold suboptimal water temperature.