Samples of atmospheric aerosol were collected at Mt. Waliguan (CGAWBO/GAW). The filter samples were analyzed by NAA (neutron activation analysis), PIXE (proton induced x-ray emission). The concentrations of 42 trace elements combined with the measurements of black carbon were determined. Based on the statistical analysis of element concentrations, enrichment factors and the principal factor analysis, combined with the corresponding back trajectory, the elemental compositions and the sources of aerosol over Waliguan are discussed. The results indicate that the natural sources identified as major contributors to the aerosol over Mt. Waliguan are the soil and crust. The factor analysis shows that the contributing rate of these sources accounts for approximately 70% or more of the aerosol. However, anthropogenic origins, such as coal burning, automobile and industrial emissions form a certain proportion of aerosol. The measurement results of the black carbon at Waliguan indicate that there exist influences from human activities. It is estimated that the pollutants mainly come from the more developed areas in the Qinghai Province and the Hexi Corridor. Both local influences, such as the elements of soil in the adjoining area, and long-range transport of aerosols can affect, in varying degrees, the composition of the background aerosol over Mt Waliguan.