Abstract: Piperaquine, with the chemical structure of 1,3 bis 4'-(7'-chloroquinoly-4') piperazinyl-1 propane, was tested in mice infected with Plasmodium berghei for its antimalarial activity.The duration of its protection against malaria was found to be directly related to the dose of piperaquine administered. It gave mice complete protection for 15 and 60 days respectively against challenge with the parasite after oral administration of 50 mg (base)/kg and 200 mg (base)/kg of the drug for three consecutive days. However, chloroquine given orally at dosage of 50 mg (base)/kg for 3 days, failedto protect the animals for 15 days.A single dose 100 mg (base)/kg and 300 mg (base)/kg of the piperaquine salts separately administered gave mice almost complete protection for 30 and 60 days, respectively.Piperaquine is also a fairly good schizonicide, as it cleared the mice of the asexual blood parasites within 72 hours after administration of 12.5 mg (base)/kg for three consecutive days. These results seem to indicate that the drug is more effective and less toxic than chloroquine.