Introduction: The certain commonly used antibiotics (cefixime, metronidazole, ciprofloxacin, cefpodoxime and cetirizine) purchased from the chemist shop in Mokokchung town, Nagaland and effects on mitotic activity of root tip meristematic cells of Allium Cepa were observed. Methods: The different concentrations were prepared by retaining the original effective concentrations (400, 400, 500, 200 and 10 mg) of the antibiotics and treated the root tips of Allium at different times (6, 12 and 24 h) to record the effects or abnormalities. Results: All the concentrations (ppm) and time (h) were effective to induce the chromosomal disturbances during the mitotic activity of root tip cells in Allium. Conclusion: The mean value (±S.E.) recorded for mitotic cells, mitotic stages, physiological and clastogenic abnormalities and showed a mixed response which could not predict dose response curve in actual.