Abstract: Ciprofloxacin was orally administered at 1.25,2.5,5 and 10 mg kg-1 body weight doses to different groups of broiler chicks on day 7,8,9, 28, 29 and 30 after the priming and booster inoculation with Ranikhet-La Sota and Sheep Red Blood Cells (SRBC) on day 7 and day 28. Haemagglutination Inhibition antibody titre against La Sota antigen and Haemagglutinin antibody titre against SRBC were observed. Ciprofloxacin in all dose levels tested showed significant reduction in antibody titre against SRBC : but did not produce any significant effect against Ranikhet-La Sota antigen.