Administration of ethylene glycol monoalkyl ethers to rodents causes acute hemolytic anemia. Metabolic activation of these chemicals to alkoxyacetic acids is required to develop hemolytic effect. Current study was undertaken to compare the hemolytic activity of isopropoxyethanol (IPE) and phenoxyethanol (PhE) in male rats. The main goal of this study was to evaluate the role of alkyl and aryl group in hemolytic activity of ethylene glycol ethers. Rats were treated subcutaneously with single doses of 0, 0.625, 1.25 and 2.5 mmol IPE/kg body weight or 0, 2.5, 5.0 and 10.0 mmol PhE/kg. At 0, 6, 24, 48, 144, 216, and 600 h after dosing, blood samples were collected from end tail of rats and various blood indices were measured. Administration of both chemicals resulted in a time-and dose-dependent swelling of erythrocytes as evidenced by an early increase in packed cell volumes and mean cell volume. Subsequently, red blood cells, total hemoglobin concentration, and packed cell volumes decreased when hemolysis progressed. Furthermore, an increase in plasma hemoglobin concentration and reticulocyte counts was observed. The onset of hemolysis induced by IPE was faster than that after PhE administration. The hemolytic activity of IPE was about tenfold higher in comparison with PhE. It is likely that the lower hemolytic activity of PhE is associated with inhibitory effect of aryl group on hemolytic action of this compound. Phenyl group, in contrast with alkyl moiety, represents electron acceptor system which exerts resonance and inductive effects and leads to changes in acid strength, also in case of phenoxyacetic acid, a metabolite of PhE.