Abstract: The Ice Nuclei (IN) were observed in Nanjing from May to August 2011 using a 5 L mixing cloud chamber and a static diffusion cloud chamber, and the characteristics of different ice nuclei concentrations were examined. The results show that during the observation period, the mean concentration of total ice nuclei measured by the 5 L mixing cloud chamber was 20.11 L^-1, the concentration of IN under high water vapor conditions (5% calculated supersaturation with respect to water) and low water vapor conditions (5% calculated supersaturation with respect to ice) measured by the static diffusion cloud chamber was 0.928 L^-1 and 0.291 L^-1, respectively. The IN under favorite conditions had a diurnal variation. The daytime concentration of IN was larger than that at night and peaked in the afternoon, which indicates that atmospheric IN is significantly influenced by turbulence intensity, human activities, and industrial pollution. The scavenging effect of precipitation on IN was obvious, and the concentration of IN increased during the typhoon system. The IN levels in the Nanjing area increased with decreasing temperatures and increasing humidity. The back trajectory model showed that the concentration of ice nuclei in the air mass from the northeast marine region was highest, and that the number of ice nuclei in different air masses decreased with decreasing activation temperature. A case analysis focused on the relationship between IN and PM₁ (the particulate matter with diameter less than or equal to 1 mm) produced by biomass burning suggested that the product of the combustion may contribute to IN.