The fruit tree Mangifera indica L. (mango tree) is known for its delicious fruits but also for the different uses of its leaves in the treatment of certain bacterial and parasitic diseases. The aim of this study is to highlight the existence of bioactive substances found in the leaves of mango trees grown in Burundi as well as their parasitological and bacteriological effects. Phytochemical screening indicated that mango leaves contain flavonoids, tannins, tannins, saponosides, terpenes, and steroids in sufficient quantities while leukoanthocyanins and quinones are in lower quantities and alkaloids are absent. The results of parasitological tests of organic and aqueous extracts prepared from the leaves of Mangifera indica L. have shown that these substances act on certain parasites, namely amoebas, flagellates (Chilomastix and Embadomonas) but inactive on hookworms, ascaris, eel and giardia. After analyzing the results of the bacterial sensitivity tests carried out on four of the extracts used in the parasitological tests, it was found that all the strains studied showed a sensitivity different from average to low for one or the other extract. Thus, those that revealed sensitivity are: Escherichia coli and Staphylococcus aureus for the tannin extract; Vibrio cholerea, Providencia stuartii and Staphylococcus aureus for the saponoside extract and Klebsiella pneumonia for the flavonoid and aqueous extracts. These results obtained in parasitological and bacterial sensitivity tests seem to justify the use of this plant in traditional medicine in the treatment, among other things, of diarrheal diseases caused by amoebas and flagellates as well as various infections caused by the various microbes tested.