The aim of this study was designed to evaluate properties and dissolution rates of sibutramine solid dispersions by spray drying. Sibutramine as appetite depressant for obesity treatment is soluble in low pH but insoluble in high pH. To improve bioavailability, it should be improve dissolution rate in pH 6.8 because sibutramine is absorbed at the small intestinal track. PVP has various molecular weights according to K values. We investigated effect of molecular weights of PVP on the release behavior of solid dispersion. DSC and XRD were used to analyze the crystallinity of the sample. It was found that sibutramine is amorphous in the solid dispersions. FT-IR was used to analyze the salt formation by hydrogen bond between sibutramine and PVP. As a result of in vitro release behavior, solid dispersion using PVP K30 is obtained good possibility of orally pharmaceutical formulation. This study proposed that this solid dispersion system controlled the release behavior according to molecular weights.