Gestational diabetes mellitus (GDM) complicates substantial number (2~10%) of pregnancies. The incidence is increasing as the rates of obesity increase. The prevalence will significantly increase if the new IADPSG recommendations are more widely adopted, although there are controversies surrounding the widespread application of them. Numerous studies have shown the direct relationship between the maternal hyperglycemia and perinatal outcomes. Therefore, the treatment during pregnancy emphasizes intensification of metabolic management by combination of medical nutrition therapy and medication. To achieve specific goals of glycemic control, between 20% to 50% of women with GDM will require pharmacologic therapy. Traditionally, insulin therapy has been considered the gold standard for the management of GDM, because of its efficacy in achieving target glucose level and the fact that it dose not cross the placenta. But, difficulty in administration with multiple daily injections, potential hypoglycemia, and increase in weight make this therapeutic option sometimes cumbersome. Since both GDM and T2DM are based on the insulin resistance and relatively decreased insulin secretion to overcome, the oral antidiabetic agents that target these defects can be alternatives to insulin therapy. Much of the concern over the use of oral agents is the lack of convincing data regarding the extent to which they cross placenta and the potentials of fetal risk. As such, the use of these medications remain issue of debate and ongoing research. Among several available oral antidiabetic agents in pregnancy, glyburide (glibenclamide) and metformin are the two most commonly used agents in the world. In this presentation, the objectives are to review available data on efficacy and adverse effects of these medications and discuss the currents gaps between research and clinical practice.