The cytological effects of the organophosphorus pesticide, Phosalone were studied on root meristems of A. cepa. Different periods of treatment were carried out using different concentrations (0.25, 0.5, 0.75 and 1.0%) of the pesticide. Subsequent Knop's recovery was done for 96 hours after treatments of upto 24 hours and 48 hours. The pesticide induced mitostatic effects on root meristem cells, the mitotic index gradually decreasing with the increase in concentration and time of treatment. Mutagenic effect was noticed with abnormalities like chromosome breakage and erosion, sticky bridges, laggrads, multipolarity, polyploidy, clumping and pycnosis. There was a slow rise in the mitotic index after recovery for 48 hours and 96 hours of 24 hours and 48 hours treatments respectively. The percentage of total chromosomal abnormalities was found to have decreased fairly in the recovery set of 96 hours of 48 hours direct treatment, the percentage of total chromosomal abnormalities was found to increase in concentrations 0.25% and 0.75% and slightly to decrease in concentrations 0.50% and 1.0% respectively. Material treated with 0.75% and 1.0% Phosalone for 48 hours, failed to show marked recovery with death of roots.