This work aims to bring out the correlation between antioxidants and antimalarial activities of secondary metabolites of Po M2 plants (flavonoids, tannins and phenolic compounds contents) and their in vitro antimalarial activity by antioxidant activities justification. Field experiments were conducted both. Seeds from to one plant of Phyllanthus odontadenius were irradiated with 150 Gy dose (M1 seeds) and cultured first in vitro following transfer of M1 plants in field. Seeds from M1 plants were cultured for obtaining M2 plants which are used as biological material in this work after their harvest. In addition, phytochemical screening was carried out using reagent methods combined with spectrophotometric methods revealed the presence of flavonoids, tannins and phenolic compounds. The in vitro antimalarial activity assays on isolate Plasmodium falciparum were determined using microscopic method revealed that the highest in vitro antimalarial activity was extracted from 1503 plants (1.43 ± 0.17 μg/mL) justified by the highest of tannin content (0.76 ± 0.13 mg/g) and ratio between IC50 from DPPH and flavonoids quantity (15.52%) and that from DPPH and total phenolic compounds (5.17%). However, ratio between IC50 from DPPH or ABTS radicals and total phenolic contents were low than these of IC50 from DPPH or ABTS and flavonoid contents for each plant extract. Evaluation of extracts antioxidant activity was determined using DPPH and ABTS as radicals. This work confirm that there is correlation between in vitro antimalarial activity and antioxidants and antiradical activities of secondary metabolites of P.o. M2 plants (flavonoids, tannins and total phenolic compounds). When IC50 for DPPH test is high, in vitro antimalarial activity is also high, and, in opposite, when IC50 for ABTS is low, in vitro antimalarial activity is high.