Abstract: Grapefruit juice was assessed for chemoprophylactic activity against Chloroquine-sensitive Plasmodium berghei berghei infection in mice. A standard inoculum of 1x106 infected erythrocytes was used to assess the prophylactic effect of grapefruit juice (15 mL kg-1) and this was compared with the prophylactic effect of high dose Ascorbic acid (150 mg mL-1 or 2.25 g kg-1). The result of the experiment showed that grapefruit juice and high dose vitamin C significantly delayed the establishment of parasitaemia compared with the control group. Furthermore, grapefruit juice and ascorbic acid prolonged the mean survival time of the mice with corresponding decreases in mean peak percentage parasitaemia, respectively. Grapefruit juice however demonstrated a stronger chemoprophylactic activity than ascorbic acid (p<0.05). These effects were however lower than the standard prophylactic drug (Pyrimethamine-1.2 mg kg-1). Regular intake of grape juice may protect against malaria infection. Further studies are necessary to elucidate possible mechanisms involved.