In order to develop natural pigments from microbes as food colorants,the production level of Streptomyces vietnamensis for violet-blue pigment was tested in different media,and such four parameters as the inoculation quantity,the culture temperature,the rotation speed and the fermentation time were orthogonally optimized.Then,the constituents of the pigment were isolated and purified by means of the silica gel column chromatography,the sephadex gel filtration chromatography,the thin-layer chromatography and the high-performance liquid chromatography,and the structure of the pigment was identified by means of the nuclear magnetic resonance and the mass spectrometry.The results show that Gauze＇s synthetic No.1 medium is suitable for the industrial production of violet-blue pigment due to its highest productivity,and that the optimal fermentation conditions are as follows： an inocu-lation quantity of 5%,a culture temperature of 30 ℃,a rotation speed of 180 r/min and a culture time of 7 d.Moreover,seven compounds,namely granaticin,granaticin B,MM44785,L-rhodinoside-deglycosylated MM44785 as well as quinizarin-derived pigments Zg,Zgg and dihydro-Zg,can be isolated and purified from the crude extract,among which dihydro-Zg and L-rhodinoside-deglycosylated MM44785 both possess novel structures.