Ocimum gratissimum Linn is a medicine herb that is used in tropical world particularly in Asia, Africa and South America. Because of the restrictions in the use of antibiotics in animal health, alternative drugs are being considered. This study was designed to assess the antibiotic activity of O. gratissimum for the control of gut microorganisms. Proximate and phytochemical analysis of the herb was carried. To 100 day old chicks, aqueous extract of the herb was administered to a set of 50 chicks (Ocimum treatment) but was not given to the second set (control). Antibiotic sensitivity testing of gut microbes (Salmonella and E. coli) isolated from the chicks was tested using 0.11 g/l dried O. gratissimum extract. In the control , the zone of inhibition (ZOI) of Salmonella was 13.2, 11.8 and 14.8mm at the crop, ileum and caecum respectively whereas in the Ocimum treatment, the ZOI were significantly higher (P<0.05)  being 15.0, 15.6 and 15.6 mm respectively. The pattern of sensitivity of Salmonella and E.coli was similar. The zone of inhibition was significantly wider in the chicks administered with Ocimum gratissimum extract compared to the control. Antibiotic activity of the herb may be due to the presence of phytochemicals particularly sapronins, alkaloids, flavonoids and tannins. We conclude by recommending the use of the plant for the control of pathogenic microbes of broilers
