Abstract: Being one of the key enzymes in the pathway of starch biosynthesis,starch synthase is important contents of starch researches which often focus on the research of its isoforms.Starch synthase includes two major kinds of isoforms, granule-bound starch synthase and soluble starch synthase, whose physiological functions a re very complicated.Based on the recent advances on enzymology and molecular biology of these isoforms of starch synthase, category，relationship and physiological functions of these isoforms in the starch biosynthesis are discussed.