In order to propose a plant extract as an alternative to the use of antibiotics used in broiler breeding, an experimental study was carried out in the department of Azaguié and the choice fell on the aqueous extract leaves of Ocimum gratissimum L (EAOG). To achieve this objective, fifty (50) broiler chicks of Cobb-500 strains were divided into two (02) batches of twenty-five (25) each. Thus, batch I received only the aqueous extract of Ocimum gratissimum L., while batch II received the prophylaxis recommended for rearing in this locality. Phytochemical screening revealed the presence of sterols and polyterpenes, polyphenols, flavonoids, alkaloids and catechin tannins in Ocimum gratissimum L. The acute toxicity study carried out on broilers showed that EAOG is not toxic by the oral route in a single dose at a dose of 2000 mg/kg BW. The EAOG caused a significant increase (p<0.05) in the live weight of the treated chickens compared to the controls. In addition, the results showed a significant reduction in the mortality rate and feed conversion ratio of chickens treated with EAOG compared to controls. Finally, concerning the biochemical and leukocyte parameters, the results showed a significant increase in the levels of urea and AST, lymphocytes, white blood cells, neutrophils and basophils of chickens treated with the extract compared to those treated with the usual antibiotics. The aqueous extract of the leaves of Ocimum gratissimum could be recommended to poultry farmers as an alternative to the usual antibiotics.