Exopolysaccharides (EPS) are natural biological polymers which are excreted outside the cell wall and infiltrated into the medium during lactic acid bacteria(LAB) growth and metabolism. It has been becoming a research hotspot recently because of its important physical properties and physiological functions, such as reducing cholesterol, antitumor, promoting thalli adhesion to intestinal mucosa, immune response and being used in foods as thickener and stabilizer. It is extremely significant to study its biosynthetic pathway, structure and structure-activity relationship for improving the EPS yield and understanding the correlative mechanism. The classification and biosynthesis mechanism of EPS, as well as their structure- activity relationship and biological activity were summarized.