Clinical bacterial isolates from chickens were analysed to determine their susceptibilities to antimicrobial agent. Ten (10) Escherichia coli and 8 non lactose fermenting Enterobacteriaceae species isolated from a pool of clinical cases of chickens from Microbiology Laboratory of the Veterinary Teaching Hospital, University of Agriculture Makurdi were used for the study. Enrofloxacin with 99 % purity obtained from Sigma-Aldriech, USA and prepared in varying concentrations (0.1 - 50μg/mL) was used in vitro by Kirby-Bauer’s disc-diffusion method. The isolates were susceptible to enrofloxacin at a minimum concentration of 25 (μg/mL) and the mean value in the zones of inhibition exhibited by Escherichia coli and non-lactose fermenters were significantly different (p<0.01). The enrofloxacin tested also exhibited the concentration dependent effect typical of quinolones in this study. The study concluded that the tested antimicrobial agents can still be applied in the prevention and treatment of bacterial infection of chickens. Usage of these agents by veterinarians in poultry with appropriate clinical judgement and proper dosing principle is recommended. Also, routine assessment of the in vitro activities of this agent against common microbial infections in this area is strongly recommended