Reform and opening-up in China brought rapid changes in the society of ethnic Koreans in China. And those changes caused following changes in language identity and language attitude of those ethnic Koreans that eventually led to change in their language use. The present study investigates relation between changes in language identity and language attitude and their language use. The rates that Ethnic Koreans living in Jilin, China consider their mother language to be Korean(Joseon language, South Korean language and North Korean language) are different by their generations. Middle aged and older people tend more to consider Korean as their mother language compared to younger generation. Those two generations, however, showed opposed opinions about the future language they will use. More of older generation predicted that Korean will be rarely used among ethnic Koreans living in China in the future compared to younger generation. The difference of language identity and the attitude to the language across generations was reflected in their actual language use. Older generations use Korean in general.They may borrow Chinese words when they can’t come up with appropriate Korean words or sometimes show code mixing by using Chinese words and sentences while speaking in Korean. In generations younger than middle age, code mixing and code switching are more frequently observed when their conversation topics are Chinese politics and Chinese cultures. The youngest generation mainly uses Chinese and showed code switching most frequently among all generations. The language use observed differently among the generations is reflection of changes in language identity and language attitude.