We conducted a study to evaluate the effect of tulsi leaf (Ocimum sanctum) extract supplementation in drinking water as a growth promoter in the broiler. A total of 50 Cobb-500 broiler chicks (day-old) were purchased from a local hatchery (CP Bangladesh Co. Ltd). After seven days of acclimatization, chicks were randomly divided into two groups:- T, (n=25) and T, (n=25). Group T, was kept as a control and untreated. Group T; was supplemented with tulsi leaf extracts 0.02% with tap water. Weekly observations were recorded for live body weight gain up to 4 weeks and hematological tests were performed at the broiler’s 21% and 28″ day’s age. The initial body weight of groups To and T, on 1% day of this experiment were 48.43+0.61 g and 47.77+0.22 g, respectively, and after the 28″ day of the experiment, final body weights were 1386.62+18.36 g, and 1476.25+12.21 g, respectively and net profit per broiler was Tk. 18.65 and Tk. 23.09, respectively. The live body weight of the treatment group (T,) was increased significantly (p<0.01) than that of the control group (To). The treatment group T, was recorded statistically significant (at 5% level) increased (6.935) live body weight than that of control group To. The hematological parameters total erythrocyte count (TEC), packed cell volume (PCV), and hemoglobin (Hb) estimation value of the treatment group was increased significantly (p<0.01), and total leukocyte count (TLC) was increased significantly (p<0.05). In contrast, hemoglobin (Fb) estimation showed significant difference from the control group. The results suggest that a broiler supplemented with 0.02% tulsi leaf extract could achieve better growth performance.