Introductionmalaria remains the leading cause of morbidity and mortality in developing tropical and subtropical nations. Due to the emergence and spread of drug resistance to currently available drugs, there is a need for the search of novel, safe, and reasonably affordable anti-malarial medications. The objective of this study was to assess the in vivoanti-malarial effectiveness of Avicennia marina stem bark extracts in a mice model.Methodsguidelines 425 of the Organization for Economic Cooperation and Development were used to determine the extracts' acute toxicity. Mice infected with chloroquine-sensitive Plasmodium berghei (ANKA strain) were tested for in vivoanti-plasmodial activity, and by giving oral doses of 100 mg/kg, 250 mg/kg, and 500 mg/kg body weight of extracts, the plant's suppressive, curative, and preventive effects were assessed.Resultsmice treated with dosages of up to 5000 mg/kg showed no evidence of acute toxicity or mortality. Consequently, it was determined that the acute lethal dosage of Avicennia marina extracts in swiss albino mice was greater than 5000 mg/kg. All doses of the extracts exhibited significant (p<0.05) dose-dependent suppression of P. berghei in the suppressive tests compared to the control group. At the highest dose (500 mg/kg), Methanolic crude extracts exerted the highest (93%) parasitemia suppression during the 4-day suppressive test. The extracts also displayed significant (p<0.001) prophylactic and curative activities at all doses compared to the control.Conclusionresults from this study ascertained the safety and promising curative, prophylactic and suppressive anti-plasmodial capabilities of the stem bark extracts of Avicennia marina in mice model.