This paper attempts to explore recent socio-demographic changes of the ethnic Korean population in Yanbian autonomous prefecture. Due to rapid decrease in the level of fertility and population ageing, Korean minority society in China has been in a process of profound transition after the introduction of the market economy and establishment of diplomatic relations between South Korea and China. The changes in demographic behaviors and in the structure of population appear to be much faster among Koreans than Hans. Results from the 2000 population census reveal that the Korean population in Yanbian, where ethnic Koreans are most densely populated in China, has been in a decreasing trends in absolute numbers and in its proportion to the total population. The growing tendency of regional mobility for work and for marriage, rapid expansion of residential areas, serious crisis of ethnic schools of Korean community, and weakening social integration and ethnic identification of Koreans in Yanbian are discussed in this study. It is expected that socio-demographic transition of Korean society in Yanbian will be even more drastic over the coming decades. The rapid changes in demographic behaviors and in the structure of population has major consequences and implications for every sphere of human life, and will present enormous challenges for the status of Korean minority society in China. Along with various statistical data on Yanbian, micro-level data as well as published reports from the 1990 Chinese population census for Yanbian and the 2000 Chinese population census are analyzed in this study. In addition to sex ratios and age ratios, various indices are calculated to analyze the characteristics and accuracy of the data from the 1990 and 2000 population censuses of China.