This study was conducted to determine the efficacy of tulsi (Ocimum sanctum) leaves extract as a growth promoter in broilers from January to June 2013 under Dept. of Pharmacology, Bangladesh agricultural University, Mymensingh-2022, Bangladesh. Fourty number of day old broiler chicks were taken and after seven days divided into two groups A and B. The B group was supplemented with tulsi leaves extract @ 1ml/litre in drinking water. Weekly observations were recorded for live body weight gain up to 5^th weeks and blood test was performed at 17^th and 35^th days age of broiler to study hematological changes between control A and treatment B group. No significant difference in hematological changes was observed in both treatment and control group in 1^st week of age but significant change in body weight gain was observed on 35^th day. They are 1500 g (control) and 1650 g (treated). The cost of production and economic study was carried out and it was observed that net profit in control group was 5.33 T.K/Kg broiler and in treatment group was 13.33 T.K/Kg broiler. Bacterial sensitivity test was positive in case of Escherichia coli and produced zone of inhibition 0.5 cm and other was negative.