Since the 1960s, we have launched a longitudinal study on the Anong language, spoken by a branch of the Nu ethnic group in Lisu Autonomous Prefecture in Yunnan Province. As researchers, we have witnessed its whole declining process. This study can serve as an exemplary case, demonstrating the forlorn hope of some endangered ethnic languages in China. Through analyzing its declining details, we not only have a good general understanding of the linguistic and social causes accounting for the changes, but also have seen the structural changes of the language in the process. In this study, we focus on the development occurred to both social milieu and linguistic structures, as well as the changes in native speakers’ attitudes towards their mother tongue. The combination of the precious study and the current analysis enables us to obtain an overall picture of the declining process from historical perspective. Based on our observation for over half a century, we conclude that the decline of the Anong language has come to a critical point, and without modus operandi of effective language maintenance, the lanuage is bound to lose its communicative function completely in one or two decades and become a dead language.