In this study, metformin HCl, a highly water soluble anti-hyperglycemic agent was prepared into tablet type with PVP of various molecular weights(Mw) to effective oral administration. Because dissolution rate of drug with Mw of PVP becomes decreased as increasing Mw of PVP. We used magnesium stearate as lubricants. We compared the in vitro release behavior of metformin from the tablets according to additives with commercial drug, Diabex(R). The change of structure and crystallinity of tablet by additives were characterized by fourier-transform infrared spectroscopy(FT-IR) and differential scanning calorimeter(DSC). FT-IR and DSC results demonstrate that structure of drug was changed and crystallinity of drug was decreased according to decreasing Mw of PVP. The dissolution rate of metformin HCl from tablet decreased in simulated gastric fluid(pH 1.2) and simulated intestinal fluid(pH 6.8) as increasing K value of PVP. This study suggests Mw of pharmaceutical exipients could effect the metformin HCl release behavior.