It's a useful measure for the protection of the endangered natural resources to extract useful substances from artificial cultured species.In this study,C-phycocyanin was extracted from liquid-cultured Nostoc flagelliforme cells with repeated frost thawing followed by frozen ultrasonic method.The crude extract was successfully purified by procedure of ammonium sulfate precipitation,ion exchange chromatography with DEAE 650M column,and gel filtration chromatography with Sephadex G200 column.The purity ratio and purity factor of the purified C-phycocyanin reached 5.321 and 7.623 respectively after successive purification procedure.It has a maximum absorption at 615nm and a maximum fluorescence emission at 646nm.There are two bands appeared at about 15.7ku and 16.8 ku for SDS-PAGE,which are attributed to α and β subunits of C-phycocyanin.The stability tests indicated that C-phycocyanin is stable in the range pH 6 to 8 with temperature below 30℃ in the dark or indoor light conditions.These results help the further study on exploitation of C-phycocyanin from N.flagelliforme cells.