Abstract: Qinghaosu (QHS) is a new antimalarial drug. Animal experiments and clinical observations indicate that QHS is highly effective against erythrocytic parasite with low toxicity and marked effect on chloroquine-resistant falciparum malaria. In order to explore the possibility of inducing resistant line of malarial parasites, we conducted an experimental study on this problem in plasmodium berghei ANKA and N strain.Using the method of "4-day suppressive test" and stepwise increasing doses of the drug in consecutive passages in mice, 2 Qinghaosu-resistant lines (RQ/ANKA and RQ/N) were developed after 58 passages during 14 months. But it failed to infect mosquitoes. The indexes of resistance (I₅₀) of RQ/ANKA and RQ/N line were 53.4 and 54.6 respectively. The RQ line exhibited Clear cross-resistance to artesunate and artemether for which the I₅₀ were 13,and 11 respectively, and a slight resistance to primaquine (I₅₀=2.8). No cross-resistance to chloroquine was found. Serial drug-free passages showed that the resistance of RQ line was unstable and sensitivity reverted towards normal after 13 passages in about 3.months.