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The experiment was carried out at Federal College of Forestry Jos, in Jos North Local Government Area of Plateau State to determine the phytotoxicity of cypermethrin pesticide on seed germination, growth and yield parameters of cowpea. Cypermethrin is popularly used by farmers as a means of treating seeds before planting to prevent insect, pest and birds attack. Randomized Complete Block Design (RCBD) involving 5 treatments T0 as control (No cypermethrin used), T1 with 0.25% cypermethrin (0.25ml of cypermethrin in 99.75ml of water), T2 with 0.50% cypermethrin (0.50ml of cypermethrin in 99.50ml of water), T3 with 0.75% cypermethrin (0.75ml of cypermethrin in 99.25ml of water) and T4 contained 1.00% cypermethrin (1.0ml of cypermethrin in 99.00ml water). Data was collected on radicle length, plumule length, number of leaves, number of branches, stem girth, number of seeds/pod, 100 seed weight, pod length and dry matter. Data collected was subjected to analysis of variance (ANOVA) at 5% level of significance using SPSS 23 and where significance was declared, Duncan Multiple Range Test (DMRT) was used to separate the means. The result of the research indicates that significance difference occurs in the radicle length (P<0.05) in which T1 has the highest mean value. The stem girth shows a significance difference with T0 having the highest mean value (7.32) at P<0.05. The result for the number of branches and the number of leaves shows significance difference with T0 having the highest mean values 39.15 and 101.65 respectively at P<0.05 level of significance. The yield parameters shows a significance difference for number of seeds/pod, 100 seed weight, pod length, as well as the total dry matter. The highest mean values for the yield parameters are observed in T0 with mean values 18.52, 18.53, 16.35 and 68.35 for number of seeds/pod, 100 seed weight, pod length and total dry mass respectively. Alpha amylase enzyme activity was observed to be higher at lower concentration of the cypermethrin (T1) on day 2 (2.75) but the increase in the enzyme activity tilted towards the highest concentration (T4) on day 3 and day 4 with mean value 2.70 and 3.10 at 5% level of significance.