Aims: The purpose of this study was to evaluate the in vitro antioxidant activities of Datura innoxia Mill. leaves and seeds harvested in Mali. Place and Duration of Study: Collection of plant materials were done at Kolondieba (Mali) in june 2016. Evaluation of polyphenols and flavonoids contents, determination of antioxidant activities were done at Laboratory of Plant and Food Biochemistry and Biotechnology of University of Sciences, Techniques and Technologies of Bamako (Mali) between august 2016 and March 2017. Methodology: The leaves and seeds were collected in Kolondieba, Mali. The phytochemical screening based on the standard methods of tube reactions has been performed with ethanol extracts. The quantitative estimation of total polyphenols was made by the Folin-Ciocalteu method and that of flavonoids by the use of aluminum trichloride. The in vitro antioxidant activities of the ethanol extracts was determined by three methods: the 1,1- diphenyl - 2- picrylhydrazyl (DPPH) test, the ferric reducing ability power (FRAP) test and the Phosphomolybdate test (PPM). Results: The phytochemical screening revealed that leaves and seeds of this plant contains alkaloids, polyphenols, flavonoids, coumarins, tannins, triterpenes and saponin. Phenolic contents of ethanol extracts are 30.97 ± 0.33 mg equivalent gallic acid / g in leaves and 14.02 ± 0.15 mg equivalent gallic acid / g in seeds; those of flavonoids are 15.13 ± 0.2 mg equivalent of quercetin / g in the leaves and 4.93 ± 0.41 mg equivalent of quercetin / g in the seeds. The three tests showed that the leaves have a higher level of antiradical activity in vitro than seeds. Conclusion: The results of this work showed that Datura innoxia Mill. has a good antioxidant activity which would justify its use as a potential source of natural antioxidants.