ABSTRACT:The in vivo study of the effect of bentonite on cyanide poisoning and its effect on plasma urea was investigated. A total of 45 wistar albino rats were used. The rats were divided into four groups and a control group. Each group had nine rats including the control. Groups 1, 2, 3, and 4 were given a daily dose of 0.4ml of cassava waste water containing a sub-lethal amount of cyanide (2.16 x 10 -3 mg). Groups 2, 3, and 4 were counter administered with 0.2ml, 0.4ml, and 0.8ml of 7% bentonite solution respectively. Administration of bentonite was done simultaneously with the cyanide administration. At the end of each week three animals were sacrificed from each group and the control and their plasma urea level determined. The experiment which lasted for three weeks showed that the sub-lethal amount of cyanide caused a significant increase (p> 0.05) of plasma urea from 0.0300 ± 0.01mmol/L per gram of rats in the control to 0.0375 ± 0.01 mmol/L per gram of rats in group 1 which was fed with only cyanide. A counter treatment with bentonite led to significant decrease (p>0.05) in plasma urea from 0.0413 ± 0.10 mmol/L to 0.0249 ± 0.01 mmol/L per gram of body weight of the rats. The reduction of plasma urea caused by bentonite was also proportional to the amount of bentonite administered. 0.2ml and 0.8ml of 7% bentonite solution caused a 5.08% and 39.71% reduction of plasma urea level respectively. This suggests that bentonite might have some preventive and therapeutic effects on cyanide poisoning. © JASEM http://dx.doi.org/10.4314/jasem.v20i3.1