The present study was investigated to study the response of onion plant genetic material to the presence of potential cytotoxic and genotoxic substances in the environment. So to evaluate the toxicity of dyeing industrial effluent collected from a dyeing industry in Surat, India, the Allium test procedure was used. 50 seeds of Allium cepa L. were taken in a petriplate and treated with 20%, 50%, 80% and 100% of dyeing industrial effluent. Tap water was taken as control. The data obtained showed that the mitotic index (MI) decreased with the increase in the effluent concentration along with diverse chromosomal aberrations. Lower concentration induced abnormality such as stickiness in chromosome, laggard chromosome and vagrant chromosome while higher concentration induced abnormality such as chromosomal bridge. At 100% concentration C-mitosis was observed.