Size exclusion chromatography(SEC)of commercially available ultrahigh molar mass polyethylene(UHMW-PE)Hostalen GUR4150 was carried out in order to determine the influence of the concentration,injected volume of sample solutions,average size of the gel particles of the stationary phase within the columns,flow rate,as well as dissolution conditions.18-Angle laser light-scattering(MALLS)and viscometric detection were used online to measure M,instric viscosity,and detect the drop in molar mass in the case of molecular degradation due to oxidation degradation and mechanical forces acting in the SEC system.A reliable method for analyzing ultrahigh molar mass polyethylene(UHMW-PE)by size exclusion chromatography(SEC)with negligible molecular degradation as was proved by comparison of on-line and off-line viscometry.The use of low bleed SEC columns,low concentration,suitbale evluent rate,and careful dissolution program.The results of UHMWPE from Hostalen and some domestic materialshave good repeatability.But some domestic materialss havent good repeatability,especially for extrusion grade UHMWPE.The rationality and representative of samples should be very important for SEC analyzing UHMWPE because less than 1 mg of samples was used in experiments.