Abstract: Objective To investigate the effects of diaphragmatic stasis expelling decoction on the multidrug resistance gene expression in transplantable tumor cells in nude mice bearing cell line HCT-8/5-Fu. Methods MTT was applied to confirm the drug resistance of human colonic carcinoma cell line HCT-8/5-Fu and the cross resistance towards other chemotherapy drugs, such as VCR, VP-16 and DDP. The model of transplantable tumor in nude mice with stable drug resistance was established by planting resistant cell line HCT-8/5-Fu into the right armpit of BABL/c nude mice without thymus. A total of 28 nude mice were randomly divided into four groups: control group, diaphragmatic stasis expelling decoction group(DSED group), 5-Fu group and diaphragmatic stasis expelling decoction plus 5-Fu group(DSED+5-Fu group). The control group received an intragastric administration of 0.9% sodium chloride solution and others received an intraperitoneal injection of 5-Fu or an intragastric administration of traditional Chinese medicine. Drug delivery was lasted for 14 days before the mice were executed. The growth of transplantable tumors in nude mice in all groups was observed. MDR-1 expression in all tumor tissues was detected by RT-PCR. Results Tumor inhibition rates of DSED+5-Fu group, DSED group and 5-Fu group were 54.9%, 32.4%, and 7.0% respectively(P<0.01). RT-PCR results showed that the expression amounts of MDR-1 mRNA in DSED+5-Fu group and DSED group were obviously less than that in control group (P<0.01). The expression amount of MDR-1 mRNA in 5-Fu group was increased slightly compared with the control group with no statistical significance. Conclusion Diaphragmatic stasis expelling decoction has inhibitory effect on the growth of transplantable tumor in nude mice with multi-drug resistance to colon carcinoma. The mechanism may be related to diaphragmatic stasis expelling decoction reversing MDR-1 mRNA expression of transplantable tumor in nude mice, therefore to enhance the sensitivity to drugs of tumor cells.