Abstract: Under increasing drug pressure, Plasmodium berghei ANKA strain developed 197.2 fold resistance to piperaquine after 9 passages during 2 months. The piperaquine-resis-tant line (PR/ANKA line) was unstable, it regained sensitivity to piperaquine after 3 drug-free passages. Through serial mice-mosquitoes-mice passages in which drug pressure was intermittently given, PR/ANKA line produced a new line (MPR/ANKA) with a resistant level of about 30-fold which remained unchanged after 10 drug-free passages at 2.5 months. The virulence of PR/ANKA line and MPR/ANKA line was markedly lower than that of parent line, but the mice infected with them didn't have the trend of spontaneous cure.MPR/ANKA line exhibited cross resistance to hydroxypiperaquine, and qinghaozhl (artesunate), the resistant index being 19.30 and 5.50 respectively. It had a slight cross resistance to pyronaridine, f.or which the index was 1.60. Towards primaquine and chloroquine, the line didn't show any cross resistance, the index being 1.07 and 0.94.