To research the pollution characteristics of aerosols during low visibility weather in Tianjin, the observational data of visibility, PM10 and PM2.5 mass concentrations and meteorological factors in the autumn and winter of 2009 were studied. At the same time a case of low visibility was analyzed to find out the evolvement processes and vertical distributions of atmospheric aerosol mass concentrations. The results have indicated that most of low visibility weather cases are in haze, accounting for half of the samples or more. Analysis of the typical low visibility process has shown that PM2.5 follows a uniform distribution in haze days with significant regional pollution characteristics. The aerosol mass concentration is increased first and then decreased in foggy days because of both hygroscopic growth of aerosols and wet clearing due to the dissolution of soluble components. PM2.5 mass concentrations in the surface layer are more than those in higher layers, depending on the vertical variation of RH and the inversion layer height.