Abstract: We have reported that ketotifen, cyproheptadinee and pizotifenum could cure mice infected with Plasmodium yoelii, and kctotifen and cyproheptadine could cure monkeys infected with Plasmodium cynomolgi. This paper presems the inhibitory effect of the above-mentioncd thrce drugs in vitro on the development of Plasmodium falciparum. 5 × 10-5M ketotifen, 1 × 10-4 M cyproheptadin and pizotifenum inhibited the trophozoites from developing into schizonts, which became degencrated 30 hours after drug exposure.