Abstract: Objective 　To study the feasibility of using TRAIL gene to treat breast cancer mediated by PEI coated magnetic iron oxide nanoparticles (polyMA G-1000) . The therapeutic efficacy was also be evaluated. Methods 　PEI coated magnetic iron oxide nanoparticles were used as gene carrier to transfect TRAIL gene into MCF-7 cells. The polyMA G-1000 without TRAIL gene was t ransfected into the tumor cells as negative cont rol and liposome mediated TRAIL gene t ransfection was taken as positive cont rol. The apoptosis of cells were detected by TUNEL method. The apoptosis ratio of tumor cells were measured with flow cytometry ( FCM) . Results 　The apoptosis of cells was demonst rated after transfecting TRAIL gene mediated by both polyMAG-1000 and liposome. The apoptosis ratio in the group with polyMA G-1000 as gene carrier were 25. 11 % ±2. 85 %, whereas it was 5. 06 % ±1. 05 % in the cont rol group with polyMA G-1000 ( P < 0. 01) . The lower apoptosis ratio of 18. 31 % ±2. 44 % was showed in the group with liposome as gene carrier ( P < 0. 05, compared with the group with polyMA G-1000 as gene carrier) . Conclusion 　TRAIL gene may induce apoptosis in MCF-7 breast cancer cells. The PEI coated magnetic iron oxide nanoparticles may be a potential gene carrier with high transfection efficacy in cancer gene therapy.