Plasmodium berghei infections which usually kill mice in 7-14 days can be terminated in most cases by administration of leaf and stem extracts of Phyllanthus amarus, in doses of 325-108.3mg/kg after inoculation of the animals with 6.2x103 parasitized red blood corpuscles. The methods employed in the course of the study were evaluation of the blood schizontocidal activity on early evaluation of the blood schizontocidal activity during established infection using mice as a case study. The 3-test showed a merozoiticidal action on Plasmodium berghei after taking 4-5µ1 of blood and preparing a thick smear and viewing with x 100 magnification. From the result obtained, blood schizontocidal activity during established infection showed a more promising result from 82.72-93.64%. Thus from all indications of my result it shows that the aqueous extract of P. amarus is therapeutically efficacious in the treatment of P. berghei in all the three test carried out in this study, and this tally closely to the claims by Nigeria Traditional healers of its effectiveness in human P. falciparum infection.