A novel water soluble nanocrystalline phthalocyanine(NNZnPc-NP)was prepared using reprecipitation method. The surface morphology,stability,singlet oxygen generation ability and photosensitive anticancer activity of it were studied by transmission electron microscopy(TEM),UV-Vis spectrophotometer and inverted fluorescence microscope.The results showed that the particle size of NNZnPc-NP is uniform,the dispersion is good,and it can be stable in aqueous solution. Besides,it also exhibits excellent singlet oxygen generation ability and photostability. The in vitro anticancer experiment results confirm that NNZnPc-NP can efficiently kill HeLa cells under the visible light irradiation. The above results indi-cate NNZnPc has good potential to be used as clinical photosensitizer for PDT.