Abstract: In wide screening thioguanine has been shown to possess moderate activity against chloroquine resistant strain of Plasmodium berghei in mice. In order to search for new antimalarial agents superior to thioguanine, a series of 2,6,9-substituted thioguanines were prepared.Preliminary antimalarial tests revealed that 2-amino-6-S-propyl(n) thiopurine (compound 3) and 2-amino-6-(S-acetonyl) thiopurine (compound 5) were more active than thioguanine against chloroquine-resistant strain of P. berghei in mice.The pharmacological studies of these Compounds will be reported elsewhere.