Fractionation technique is very significant for the polymer analysis. Several methods were proposed, SEC(Size Exclusion Chromatography), FFF(Field Flow Fractionation), Electrophoresis, Hydrodynamic Chromatography, MTF (Molecular Topology Fractionation), and so on. In these methods SEC is the most general. This report reviews about concepts of separation mechanism, sources of analytical error, detectors, and analysis examples of SEC.