Multidrug-resistance (MDR) is a major hindrance to successful chemotherapy. The emergence of MDR is multi-factorial. Among them, the MDR1 gene/P-glycoprotein (P-gp) is a popular and important reason. In our study, an MDR1 single-factorial drug-resistant leukemia cell line K562/MDR1 was constructed via transferring full-length human MDR1 cDNA into drug-sensitive K562 cells. The short-hairpin RNA (shRNA) targeting MDR1 gene was transfected into K562/MDR1 cell lines by the replication-defective lentiviral vector derived from HIV-1. The efficiency of RNA interference (RNAi) to silence the MDR1 gene and reverse multidrug-resistance in the MDR1 single-factor drug-resistance cell line K562/MDR1 was evaluated. The multi-factor resistant cell line K562/A02, induced by doxorubicin exposure, was used as a control. After RNA interference, the expression of the MDR1 gene and P-gp in K562/MDR1 was markedly down-regulated and the drug sensitivity was restored as IC 50 values became similar to the K562 sensitive cell line. The expression of the MDR1 gene and P-gp in K562/A02 was markedly down-regulated too, and drug-resistance to anticancer drug is reduced to some extent but the IC 50 was significantly higher than that of the sensitive cell line. These results demonstrated that lentivirus-mediated RNAi could efficiently downregulate the expression of MDR1 and Pgp, and successfully reverse a cell's resistance to chemotherapeutic. Due to only MDR1 resistance, the K562/MDR1 cell showed much high specificity and thus is a better cell model for MDR1/P-gp research.