Abstract: Glycine betaine is one of the nontoxic and organic osmolytes which can accumulate rapidly in many plants under salt and other stresses. It plays an important role in maintaining osmotic balance and protecting some important enzymes in plant cells. Introduction of the synthesis pathway of glycine betaine into plants has been one of the most promising ways to improve their salt tolerance. The biosynthsis pathway and physiological functions of betaine and the progresse s in genetic engineering of the enzymes involved in its synthesis are discussed.