Plants are direct recipients of agro-toxics and therefore important materials for assessing environmental chemicals for genotoxicity. Three doses, representing ¼, ½ and EC50 of all the eight pesticides were assessed for cytotoxic and genotoxic effects. The genotoxic effects of onion root tip cells to some common pesticides and the chromosome aberration assay were carried out after 24 h exposure. Cytotoxicity was inferred when the Mitotic index (dividing cells/1000 scored) of treated cells was ½ negative control. All the pesticides were found to be toxic. Genotoxicity was measured by analyzing 30 to 100 anaphase-telophase cells per dose of chemical for chromosome fragments, bridges, vagrant chromosome, c-anaphase, multipolarity and stick chromosomes and comparing the percentage of aberrant cells at each dose with that of the negative control. With the exception of Dieldrin, all the other pesticides were found to be genotoxic. The C-anaphase and Stick chromosomes and all the types of aberrations were predominated which was evidence of the action of the pesticides on the mitotic spindle and the coiling of chromosomes during anaphase to telophase.