Effect of chemical mutagens was studied in mitotic cells of Allium cepa L. For this purpose root tips were treated with saturated solution of peradichloro benzene, 0.2% EMS and 0.2 % freshly prepared colchicines for 4hours to 9hours.The studies revealed a wide range of chromosomal abnormalities such as stickiness, laggards, chromosomal bridge, unequal separation, nuclear budding, multinuclear cells etc.The parentage of chromosomal abnormalities in different mitotic stages were calculated on mitotic index, frequency of phases and percentage of abnormalities in mitosis. The chromosomal abnormalities increase with increase duration of treatment. The results showed that in colchicines and EMS more than 50% abnormalities ware observed after 8 hrs of treatment, while in PDB it takes 6 hours treatment. Minimum MI was recorded as 65% in controlled cells. In colchicines and EMS treated cells 0.9.5%, 20% MI ware observed after 8hrs of treatment. Whereas in PDB maximum 23% MI was recorded in cells treated for 6hrs.