Abstract: In this paper,using purple sweet potato extract and milk powder as main materials,a new kind of yoghurt with bright color,favor and nutrition was produced.p H,acidity,viscosity,and the bacteria content at the end of fermentation were taken as indexes to analyze the effect of purple sweet potato extract on property of fermented milk.The addition of the extract of purple potato led the decrease of the initial and fermentation p H,and viscosity,while increased acidity and bacteria content in the fermented milk.On the basis of the sensory evaluation systems,the process conditions of purple potato yogurt were optimized to be 16 mg / mL purple sweet extract,8% sugar and 4.75 h fermentation time.The flavor substances of purple potato yogurt were then measured by GC- MS. Compared with yogurt without adding the extract of purple potato,terpenes,hydrocarbons,furan substance,and sulfocompound can be tested only in purple potato yoghurt.The results may be helpful to the development of the new type purple potato yoghurt.