P>Objective To explore a new approach to prepare magnetic gemcitabine stealth nanoliposomes（MGSL）， and evaluate its quality and its antitumor effects EM>in vitro/EM>.  Methods MGSL was prepared by reverse-phase evaporation method. The coated rate, shape, diameter, distribution of MGSL were examined by high performance liquid chromatography(HPLC), microscopy and laser light scattering. Then the stability of MGSLs was also evaluated. The antitumor effect on breast cancer cell line MCF-7 EM>in vitro/EM> was investigated. Electron microscopy was employed to observe morphological features and ultrastructure changes of apoptosis of MCF-7 cells. The effect of MGSL on proliferation inhibitory rate of MCF-7 cells was measured with MTT method. The FCM analysis was carried out to examine the cell cycle distribution and cell apoptotic rate. Results The electron microscope and atomic force microscope photographs of MGSL showed that the shape of liposome was round or elliptical. It was showed that 97.62 percent of the liposome optimized was 206.6nm with above the coated rate 81.7%. Moreover, it possessed a good magnetic response and a high stability. MCF-7 cell line was sensitive to MGSL and the cytotoxity was correlated with the loaded drug dose. After treated for 2h, the effect of MGSL on proliferation inhibitory rate of MCF-7 cells was lower than that of gemcitabine group（EM>P/EM><0.05）, while treated for 48h, the effect on proliferation inhibitory rate was similar（EM>P/EM>>0.05）. Moreover, the effect on proliferation was also similar between MGSL group and MGL group（EM>P/EM>>0.05）.The effect of apoptosis of MGSL on MCF-7 was obvious and the rate of apoptosis was 51