The herbicides Thiobencarb and Dithiopyr are largely used as weed killers, especially in the rice fields, where cultured tilapia can be exposed to the adverse effects of such herbicides. Leaching of the herbicides in the soil could also affect the wild fish in the natural habitats and so considered as chemical water pollutants. To assess the adverse effects of these herbicides on the Nile tilapia in this study; Lcso was determined and recorded as 720jig/l and 280jig/l for Thiobencarb and Dithiopyr respectively. Nile tilapia were exposed to acute and chronic exposures of Thiobencarb and Dithiopyr as single and mixed treatment^ 'The residue of both herbicides in fish tissues was estimated, and revealed that the highest value was detected in the liver, while the lowest was in the brain. Biochemical and genetic studies were applied to evaluate the toxicity and alterations due to Thiobencarb and Dithiopyr in Nile tilapia. deviated values of serum and muscle total protein and alkaline pho&phatase were observed in acute and chronic cases with a synergistic action in the case of the combination of the two herbicides. Concerning genetic studies, utilization of the apoptosis technique in vitro resulted in apoptotic bands in. the spleen, kidney, and liver. This result was confirmed by the micronuclei findings, which indicated an alteration of the cell division in gills as a naturally exposed organ to the polluted water in case of acute and chronic exposure/The histopathological studies revealed frequent degenerative changes in the parenchymatous organs, widespread necrosis and activation of the melanocytes and the severity of changes appeared in the long-term exposure to mixed Thiobencarb and Dithiopyr. However, this study confirmed the cytotoxicity of the two largely used weed controllers, Thiobencarb, and Dithiopyr on the Nile tilapia.