The challenges posed by microbes in poultry industries and the continued search for natural means of combating them inspired this study. The effect of  the stem bark extracts of Anacardium occidentale on avian colibacillosis was investigated. Ethanol and aqueous extracts of the stem bark of A. occidentale  were prepared using standard methods. In vitro antimicrobial activities of the extracts were evaluated against E. coli. Nine groups of 10 broilers (day old  chicks; 48 g – 50 g) each were created and bred for a period of eight weeks. Groups 1 to 3 served as the control, while group 4 to 9 served as the test  groups. Meat quality, biochemical and haematological assessments were done using standard methods. The maximum zone of inhibition observed was  13.0±0.4 mm at 100 % concentration of the ethanol extract. Both extracts were observed to have a bactericidal / bacteriostatic ratio of 2. The extracts  improved the meat quality, blood protein, liver enzymes and renal functions of the broilers compared to the negative control. Again, packed cell volume,  haemoglobin and red blood cell counts were increased by the extracts compared to the negative control. On the whole, the results obtained for the  extracts were not significantly different (p > 0.05) from that of the commercial antibiotics (positive control) results. Therefore, we can infer that crude  extracts of A. occidentale could be used against Colibacillosis disease in place of the conventional commercial antibiotics.