Characgcteristics of nocturnal boundary layer (NBL) were analyzed by the upper-air observations data using with the airsonde and pilot balloons from 1994 to 1999 in Kyungpook province. The automatic weather system was also installed to obtain data in the surface layer. The atmospheric boundary layer can become stably stratified when the surface is cooler than the air. Stable nocturnal boundary layer heights were estimated from the top of surface stable layer where the vertical gradient of temperature and mixing ratio tend to zero or negative. The depth of the stable nocturnal boundary layer depended largely on the thermal effect rather than the wind effect at nighttime. The NBL was more developed on the land than on the coastal region. The stability index (bulk Richardson number) showed that the NBL was stable when the wind was weak and the vertical gradient of the temperature was strong. The heat budget in the NBL was studied by considering the effect of the radiative and the turbulent cooling rates in the cases with cloud and without cloud. The NBL under clear sky was cooled by both the longwave radiative flux and the divergence of the heat flux, while NBL under the cloudy sky the longwave radiative flux played a role of the warming. It was noted that the heat was not conserved in both cases. To complete the heat budget in the NBL the warming/cooling by advection and subsidence must be considered.