Vincristine (VCR) encapsulated in phospholipid micelles (micellar VCR) were made of polyethylene glycol phosphatidyl ethanolamine (PEG-PE) to improve its effect of growth inhibition on breast tumor cells and to decrease its drug toxicity. The morphological examination of micellar VCR was performed by transmission electron microscope (TEM). The mean particle size and size distribution were determined by dynamic light scattering (DLS). The entrapment efficiency and release behavior of VCR in micelles were investigated by reversed-phase high-performance liquid chromatography (HPLC). The MTT method was employed to test the cytotoxicity of VCR-encapsulated micelles and free VCR in the MCF-7 cells. The micellar VCR exhibited an irregular spherical shape from TEM photographs. VCR can be efficiently encapsulated in PEG-PE micelles that having high entrapment efficiency (95%) when using the molar ratios of VCR/PEG-PE from 1∶2 to 1∶10. The mean diameter of the micellar VCR was (11.1±0.1) nm with narrow size distribution. The results of release and dilution experiments indicated that the micellar VCR was stable in both HBS and serum (pH 7.0), and the release profile of VCR from micelles can be well described by one-order kinetic equation (r = 0.9997). The cytotoxic activity of VCR encapsulated PEG-PE micelles demonstrated high inhibitory effect on MCF-7 cell growth compared to the free VCR. It is concluded that VCR encapsulated in PEG-PE micelles were stable and have high drug entrapment efficiency and high effect of growth inhibition in vitro. PEG-PE micelles may be promising vectors for delivery of VCR into tumor in vivo.