Based on the observational data obtained from the 200 m meteorological tower in the urban area of Nanjing, together with the L band radar and conventional observational data, a comparative analysis of the boundary layer structures of two fog events in the autumn of 2010 is conducted. The results are:(1) The fog occurred on 17 November was a typical radiation fog, but that on 21 November a typical advection fog. (2) There existed a thick temperature inversion layer for both radiation fog and advection fog at lower levels; during the radiation fog, there was multilayer and subsidence inversion, but during the advection fog, there was single layer inversion due to warm airflow in the boundary layer. The intensity of temperature version during the radiation fog was stronger than that during advection fog, and there was an upper temperature inversion during the development of both.(3) The development of both fog had a close relation to the evolution of the surface temperature: after the sudden drop of surface temperature and the quick stronger intensity of temperature inversion, the relative humidity of the boundary layer increased more significantly, and the fog got thicker. The height of fog top during radiation fog was much higher than that of advection fog.(4) The wind velocity in the boundary layer displayed a peak valley variation. There was a certain relationship between wind velocity fluctuation and fog development:when the wind velocity decreased obviously, the fog got thicker; with the strengthening of turbulence, the fog tended to clear away.