Herbicides have, no doubt, increased crop yields by killing different types of weeds, however, rainfall and irrigation can wash herbicides from sites of application into the water system. Fish has an important role in the food chain; therefore, investigation of the effects of Round-up on fish has a diag-nostic significance in evaluation of adverse effect of herbicides to human health. The sub-lethal effects of Round-up herbicide on juveniles of an Afri-can catfish Clarias gariepinus was investigated under laboratory conditions. The herbicide caused mortality of fish in a concentration dependent manner for the duration of exposure to acute concentrations (LC5O) of the herbicides for 96hrs.The lethal concentration (LC5O) value of glyphosate was gotten to be 0.560mg/1 for 96hr of exposure using Probit analysis. For the sub-lethal assay, standard haematological procedures were adopted to evaluate the blood parameters. There was significant reduction (p<0.05) in WBC, HGC, RBC, Lymphocyte and Monocyte in order of concentrations with respect to the control. There was also a significance increase (P<0.05) in MCV, MCH, MCHC and Platelet in order of concentration with respect to the control. The results of the biochemical properties showed that the level of total protein, glucose and total cholesterol were elevated with increase in concentration on exposure period of 8weeks compared to the control experiment(P<0.05). This clearly shows that the values were dose-dependent. The result from this study shows that Round-up has a toxic effect on C. gariepinus. This toxicity can end up in humans through the food chain.