In this study, changes of erythrocyte morphology of Tilapia (Oreochromis mossambicus, L.1758) exposing to the different concentrations of lead have been investigated. Fish were exposed to low (0,5 mg L-1 ), medium (2,5 mg L-1 ) and high (5 mg L -1 ) lead concentrations semi-statically during 14 days. At the end of the experiment, important changes in the treatment groups exposed to medium and high lead concentrations were shown than the control group (p<0.05). Medium and high doses of lead red blood cell nucleus area, an important reduction in the length and width compared to the control, while the width of the cell cytoplasmic space and the control group showed a significant increase (p<0.05).