In 1988, 50 cases each of falciparum malaria were treated by dihydroartemisin (360 mg in 5 days and 480 mg in 7 days respectively), and compared randomly with piperaquine phosphate group. The results showed that the plasmodium of falciparal malaria in Dong Fang County, Hainan province, is much more resistant to piperaquine phosphate, in the 51 cases treated by piperaquine, 33.3% were sensitive, 19.0% were RI, 21.6% were RII, and 25.5% were RIII. The effect of dihydroartemisinin (both 5 days and 7 days therapy) were obviously better than that of pipera quine, fever subsidence time and parasite clearance time were similar and parasite recrudescence rate showed no obvious difference in these two groups too.