Abstract: Study on the fermentation of Nan Feng orange by lactic acid bacteria, the changes of colony-forming units, pH, total acid, organic acids and sugars with the fermentation time were determined. The changes of vitamin C, flavonoid and polyphenol were also analyzed by the ultraviolet spectrophotometry. It was shown that lactic acid bacteria could be better adapted to the environment of orange juice fermentation and grow well. The total acid content increased during the whole fermentation. The pH value was reduced to 3.2 after fermentation. The content of sugar, fructose and glucose decreased with the fermentation time gradually. Citric acid, malic acid and acetic acid were easily metabolized and were decreased during the fermentation. As the major metabolic product, lactic acid was rapidly increased from 0.44 mg/g to 13.05 mg/g during the fermentation (p<0.05). Short chain fatty acids increased from 5.23 mg/g to 13.05 mg/g by fermentation. Vitamin C remains above 80%, however flavonoid and polyphenol were dramatically increased and improved to 12.9% and 8% respectively (p<0.05). The constitute of flavor amino acids after fermentation changed and the total of amino acids decreased 13.9%. Lactic acid bacteria can be used for Nan Feng orange juice fermentation and flavor, nutrition and health care can be largely improved after fermentation.