Varying levels of Ocimum gratissimum were added to the diet of juveniles of Clarias gariepinus to ascertain its effect on the haematological profile of experimental fish. The study which lasted for 4 months was conducted using 15 concrete tanks of dimension 1m x 1m x 1m. One hundred and fifty juveniles of C.gariepinus used were acclimated for three days and distributed in 10s per tank which were grouped in triplicates, to form five treatments (1 - 5). Treatment 1, served as the control. The diets contained 0g, 10g , 20g, 30g, and 40g of O. gratissimum per kg of 2mm Coppens feed and labeled Diets 1 - 5 respectively. Fishes were fed rations of 3% body weight twice daily, with diets having corresponding numbers with the tanks. Blood samples were taken from one fish in each treatment at the end of the culture period to determine the blood quality of the fish in each treatment. Data collected were subjected to correlation analysis, one way analysis of variance and means were separated using Duncans multiple range test. C. gariepinus fed 10g inclusion of O. gratissimum performed better haematologically with an increase in Red Blood cell, White Blood Cell, Plasma protein, and Mean Corpuscular Haemoglobin Concentration. It is therefore concluded that the optimum level of inclusion of O. gratissimum to achieve improved blood quality and boost immunity is 10g/kg of feed.