Drug resistance in Plasmodium falciparum is a serious problem in most endemic areas. Recent studies have suggested the potential involvement of genes in the MDR gene family in resistance to quinoline-containing compounds in P. falciparum. In our present studies, a molecular analysis of pfmdr 1 in isolate strain of P. falciparum, 523a R, from Japanese mefloquine-resistant patient was done to determine the reported association of pfmdr 1 intragenic alleles and mefloquine resistance, and to examine the antimalarial activities of several antimalarial agents against the P. falciparum strain. The antimalarial activities against the strain was decreased susceptibility to mefloquine, artemisinin and halofantrine, in contrast increased susceptibility to chloroquine. The DNA sequence analysis of pfmdr 1 gene in a strain reveled no association of intragenic alleles with mefloquine resistance. Furthermore, the overexpression of pfmdr1 mRNA have been observed and it is about 7.2 times higher than sensitive strain. Our data shows that overexpression of pfmdr1 gene may be associated in mefloquine-resistance mechanism.