Aims: To screen for the presence of bioactive antioxidant phytochemicals and determine the antioxidant activity of Detarium Senegalense root bark. Place and Duration of Study: Department of Biochemistry, Michael Okpara University of Agriculture, Umudike, Nigeria, between April 2018 and December 2018. Methodology: Two solvents, water mixed with chloroform (70:30) was used for extraction. The plant extract was screened for the presence of phytochemicals by standard qualitative analysis and evaluated for in vitro antioxidant activity by determining the reducing power, total antioxidant capacity, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and nitric oxide radical scavenging activity in comparison with ascorbic acid and gallic acid. Results: The reducing power and nitric oxide scavenging activity of the extract increased in a concentration/dose dependent manner and was significantly (P<.05) lower when compared to ascorbic acid and gallic acid at all concentrations tested. The total antioxidant capacity (TAC) of the extract also increased as the concentration increased. Interestingly, at 1000µg/ml, the extract (201.45±0.95) was found to be significantly higher (p<.05) than that of ascorbic acid (198.36±0.83), although lower than gallic acid (266.50±0.84). The % DPPH inhibition of the extract was also significantly lower when compared to ascorbic acid and gallic acid at all concenterations tested. Overall, the results showed the extract was able to scavenge free radicals in a dose dependant manner and revealed the presence of tannins, steroids, alkaloids, terpenoids, saponins and phenols whose synergistic effect may be responsible for the antioxidant activity of the extract. Conclusion: From the study, it is concluded that the aqueous extract of Detarium Senegalense root bark possess appreciable/considerable antioxidant properties and could be exploited as source of antioxidant additives or supplements. However, there is need for further work to clarify and isolate the different classes of phytochemical constituents and also to investigate it’s in vivo potential.