Objective: To observe the effects of chemosensitizer on expression of P-glycoprotein (P-gp) in multidrug-resistant (MDR) carcinoma cells and the changes of corresponding 99Tcm-MIBI (referring to methoxy isobutyl isonitrile) uptake kinetics. Methods: Firstly, the immunocytochemistry was used to test the experssion level of P-gp in carcinoma cells; then the γ counter was used to test the uptake rate of radioactive precipitation of 99Tcm-MIBI; and finally to do statistical analysis of the test data. Results: The P-gp expression in MCF-7/S cells was negative, while it was strongly positive in MCF-7/ADM cells, and the P-gp expression in MCF-7/ADM cells reduced significantly after the tetrahydropalmatine (Tet) effect. The uptake rate of MCF-7/S cells reached the maximal value (1.39%) after being cultured with 99Tcm-MIBI for 90 minutes, and then it kept in equilibrium. The 99Tcm-MIBI uptake rate of MCF-7/ADM cells had been maintained at low level, being 0.371% after 90 minutes. The 99Tcm-MIBI uptake rate of MCF-7/S cells was higher than that of MCF-7/ADM cells. After the tetrahydropalmatine and verapamil effects, the 99Tcm-MIBI uptake rate of MCF-7/S cells had no significant change, while the 99Tcm-MIBI uptake rate of MCF-7/ADM cells increased by 1.9 times. Conclusion: Tet can reverse the MDR in MCF-7 cells, and the mechanism can achieve the effect of reversing the drug resistance through adjusting down the expression of P-gp in carcinoma cells.