Abstract—In vivo antimalarial activity of the crude aqueous bark extract of Trichilia monadelpha was evaluated using chloroquine-sensitive Plasmodiumberghei berghei infection in mice with a view to finding scientific evidence for the use of the plant as traditional antimalarial remedy in Ido/Osi LGA of Ekiti State, Nigeria. The crude aqueous extract of Trichilia monadelpha (100, 200 and 500 mg/kg) was administered orally to mice infected with Plasmodium berghei berghei in both early and established infection. The antiplasmodial effect during early and established infection of the plant in blood was determined. The extract at these doses caused 50-61% activity during early infection and 7.3-24.6% activity during established infection when compared with negative control. Chloroquine produced 100% activity. In both tests percentage parasitaemia still rose but not as high as that of negative control group. Trichilia monadelpha seems not to produce a curative effect on malaria but suppresses malaria to a certain degree.