Abstract: The genotoxicity of sewage water samples was investigated using the Allium root chromosomes assay. Sewage influent (untreated) and effluent (primary treated) were used to treat Allium cepa bulbs in 1995. The treatment with both sewage waters and their dilutions decreased the mitotic index and increased the aberration rate of dividing and nondividing cells significantly than the control. Sewage water from the West Plant caused the highest rates of chromosomal abnormalities due to its pollution from industrial activities. It was recommended that sewage water needs further treatments to remove or lower the pollutants as heavy metals before being used.