Resumo. The objective of this present study was to investigate the haemato-biochemical indices and intestinal microbial population of broiler chickens fed diets supplemented with Prosopis africana (African mesquite) essential oil (PAEO). A total of 540 one-day old broiler chicks of Ross 302 strain were allotted to six treatments with 6 replicates consisting of 15 birds each in a completely randomized design. Feed and water were given ad libitum, and all necessary management practices were strictly observed throughout the experiment, which lasted for 8 weeks. The birds in treatment 1 (T1) was fed a basal diet with no PAEO, T2 was fed basal diet plus 1.2 g kg-1 Oxytetracycline, T3, T4, T5 and T6 were fed basal diet plus PAEO at 200 mg, 400 mg, 600 mg and 800 mg kg-1 respectively. All haematological parameters and intestinal microbial population were influenced by the dietary treatments (p ˂ 0.05). Total protein, triglycerides, cholesterol and urea were significantly different (p < 0.05) across the dietary treatments and are within the physiological ranges reported for healthy chicken. However, serum tryglycerides, low density lipoprotein, high density lipoprotein, magnesium and chloride ion values were not affected by PAEO (p ˃ 0.05). It was concluded PAEO possess several properties – antioxidant, antimicrobial, hepatoprotective, immune-stimulatory, anti-inflammatory and physiological amongst others all of which are vital for the health enhancing effects in birds. Prosopis africana essential oil can be supplemented up to 800 mg kg-1 in the diets of broiler chickens without causing any deleterious effect on their blood profile.