Paper-mill effluents was examined for its cytotoxic nature using Allium cepa L. root meristems, Cytotoxicity of the effluent was investigated by treating onion root with different concentrations of effluent (25%, 50%, 75% and 100%) for 24, 42 and 72 hours. Simultaneously the physicochemical properties of such effluent’s sample were also analyzed for common parameters. The effluents inhibited cell division at strong dosage effect was observed from a decline in mitotic index with increase in effluent concentrations and duration of treatment. The effluent was also induced various mode of mitotic anomalies, such as laggard, fragmentation, stickiness and bridge etc. were observed. Observations of the present investigation revealed that the Paper-mill effluent acts as a cytotoxic /mutagenic agent at high concentration.