Abstract: The effect of chemical mutagens on the induction of mitotic chromosomal aberrations in diploid Allium cepa and tetraploid Allium vineale has been studied. In inducing chromosomal aberrations in case of both diploid and tetraploid Allium all the mutagens were found to be effective . Mitotic irregularities were higher in tetraploid species as compared with the diploid species. All types of chemical mutagens were found to be effective for the induction of chromosomal aberrations but chromosomal aberrations are increased due to the effect of Ethyl Methyl Sulphonate (EMS) in comparison to the other chemical mutagens. In explaining the concentration of EMS application of 0.20 % of the chemical may be the highest dose whereas 0.05 % may be considered as a lower dose.