The effect of long-term administration of methomyl on clinical symptoms some organs weight gain, enzymes activities and chromosomal aberration was studied male of albino rats male albino rats (Rattus norvegicus) treated with methomyl soluble powder (90%swp) during the experimental period (90 days) by different concentrations (5,10 and 20ppm) that dissolved in drinking water and also the effect of recovery period (30 days) were studied methomyl induce clinical symptoms of toxicity in the different concentrations included lacrimation, convulsion ,hypertension was increased with higher concentrations, where as 5 ppm produced slight symptoms.  The organs weight ratio of treated albino rats with 5, 10 and 15 ppm were increased respectively.  On the other hand, in treated rats by different concentrations of methomyl data cleared that the urea and creatinine levels in the treated rats during the experimental period The maximum increase observed in the case of kidney function after exposure to 20 ppm with methomyl.  In contrary, a slightly inhibition which correlated with the concentration 5 ppm was observed in the cholinesterase activity (BChE) in plasma of rats.The highest chromosomal aberration was observed in treated rats with 1/20 and 1/10 of LD50 doses after 12 and 18 hrs, while the lowest chromosomal aberration was noticed after different intervals in treated rats for 1/40 LD₅₀ methomyl.