Based on the data of aerosol chemical compositions obtained at WMO GAW (World Meteorological Organization Global Atmospheric Watch) station in eastern China－Lin’An regional background air pollution monitoring station, two methods (referred as Malm method and Stelson method) that were described by Malm (Malm et al.,1994) and Stelson (Stelson and Seinfeld, 1981) were used to study the mass closure (or mass reconstruction) of sampled aerosols. The inter-comparison of reconstructed aerosol masses with the gravimetric masses showed good agreements, although the two methods used different chemical composition species. The mass closure indicated that both methods could identify most of aerosol masses sampled during the experiment. This study suggested that based on the interests or objectives of the specific study, both of the Malm method and the Stelson method could be used for the aerosol mass closure.