Abstract: Objective: To investigate the reversal of topotecan resistance by MRP3 antisense oligonucleotide (ASODN) on topotecan-resistant SKOV3/TPT cells. Methods: A 22-base antisensephosphorothioate oligonucleotide for MRP3 was artificially synthesized that included the translation initiation site. The sense oligonucleotide (SODN) corresponding to the ASODN was also synthesized as a control. Lipofect-2000 (LF) was used for the transfer of either ASODN or SODN into SKOV3/TPT cells. The resistance index of topotecan, intracellular fluorescence intensity of TPT and changes of MRP3 mRNA expression in transfected SKOV3/TPT cells were detected by methyl thiazolyl tetrazolium (MTT) assay, flowcytometry (FCM), and semiquantitative reverse transcription-polymerase chain reaction (RTPCR), respectively. Results: The transfer of MRP3- ASODN/LF into SKOV3/ TPT cells resulted in: (1) a decreased resistance index to topotecan from 10.67 to 3.165. (2) an obviously increased intracellular TPT fluorescence intensity from 4.55±0.75 to 9.05±.13 (P<0.05); (3) Reduction of MRP3 mRNA level (60.16%)(P<0.05) in SKOV3/TPT cells, as compared with non-transfected cells. No significant change could be detected after transfecting SODN or LF alone. Conclusion: ASODN transfection may partly reverse MRP3-mediated drug- resistance of ovarian cancer cells to TPT.