Abstract: Objective To study the mechanism of drug resistance of human lung adenocarcinoma multidrug-resistant cell line Anip973/NVB. Methods Immunohistochemical technique was used to detect the expression of P-gp and MRP.Gene expression of MDR1 and MRP3 were detected by RT-PCR. Results The overexpression of MRP was detected in Anip973/NVB cells,but not in Anip973 cells.The RT-PCR results showed in Anip973/NVB cells the transcription al level of MRP3 was higher than that of control and no transcription of MDR1 was detected. Conclusion MRP3 was overexpressed in lung adenocarcinoma drug resistant cells line Anip9731 NVB.The mechanism of drug resistance of Anip973/NVB may be relatied with the overexpression of MRP3.