Malaria is one of the world’s most deadly infectious diseases. Spread and emergence ofrnantimalarial drug resistance is the major challenge that endangers all the recent gains in malariarncontrol. Medicinal plants are the key source of new effective antimalarials. Syzygium guineensernis commonly used by traditional healers’ in many parts of Africa including Ethiopia for treatmentrnof malaria. Thus, this study attempted to evaluate in vivo antimalarial activity of 80% methanolrnextract of the stem bark of the plant in mice infected with Plasmodium berghei ANKA strain. Tornthis effect various doses (100, 200, 400 mg/kg) of the extract were evaluated for the antimalarialrneffect using the four-day suppressive, curative and prophylactic tests. Parameters, includingrnpercent parasitemia, survival time, body weight, body temperature and packed cell volumern(PCV) were determined using standard procedures. A significant (p