Abstract: The ice nuclei concentrations were observed using a Bigg type mixing cloud chamber in the spring seasons of 1995 and 1996 at Beijing. The day to day changes of ice nuclei concentration were analysed. These observations have also been compared with the similar observations in 1963. The preliminary results show that the ice nuclei concentrations at Beijing have increased by fifteen times from 1963 to 1995 and are extremely high during heavy pollution conditions. The region with high concentration of IN was very large inferred by the relationship between visibility and IN concentration. It implied that the impact of human activities the as an important factor of ice nuclei source has been intensifing from 1963 to 1995. The analysis also showed that the existence period of higher activity IN(-15 to -20 ℃) was shorter than that of lower activity IN(-25 to -30℃).The vertical distribution of IN concentration with different activity was inferred by the relationship between IN activity and particle size, showing that the higher activity IN decreasing with height might be more rapid than that of lower activity IN.The relationship between ice crystal and aerosol particle concentrations was analysed using the results observed by aircraft with particle measuring system (PMS) in ice-clouds. The analyses show that a positive correlation can be established between them. Usually the ice crystal size distribution was narrower in the ice clouds with high ice crystal concentration than that with low ice crystal concentration,and the peak diameter of ice crystal was smaller. It implies that the ice nuclei concentration might play an important role to the microphysics structure of ice cloud. In this paper a comparison was made among the results observed at different places in the world and using different observing methods. Some differences of characterisitics among them were discussed preliminarily.