The effects of two different kinds of wastewater samples, taken from olive oil and milk industry were investigated in the mitotic cell division in onion (Allium cepa) root tip cells during germination. Our pretreatments showed that olive oil industrial wastewater was more toxic than milk industrial wastewater. Thus we prepared different concentrations of milk industrial wastewater solutions (100%, 75%, 50%, 25%) and olive oil industrial wastewater solutions (20%, 10%, 5%, 2.5%) using modified Hoagland nutrient solution. Control groups were germinated in modified Hoagland nutrient solution. As a result all the concentrations used caused several abnormalities in mitotic cell divisions and decreased the mitotic frequency in the onion root tip cells. Chromosomal bridges, laggard chromosome, polar slip and lack of cytokinesis and some other abnormalities were observed in different phases of mitosis. Furthermore, we also observed the negative effects of wastewater samples on chromatin condensation in the interphase