The purpose of this study is to investigate and analyze the language use patterns of Korean-Americans by comparing the characteristics of 1st, 1,5th and 2nd generation in the USA. The data revealed that there is significant difference between the perception on the necessity of the language proficiency and the perception on the language identity. Korean Americans perceive the necessity of English proficiency is slightly stronger than the necessity of Koreanproficiency. This result reflects that Korean Americans generally put more importance on the language of their residential country and it is not different from the previous research results on Korean residents in China and the CIS. However, the percentage of Koreans who perceive Korean language as their mother tongue is higher in the US, comparing to China and the CIS. Therefore, Korean Americans show more positive perception on Korean language and culture than English and American culture. Based on the analysis by the immigrant generation variable, the first-generation immigrants show high proficiency in Korean language in all areas, whereas the second-generation immigrants show the opposite results. For the 1.5th generation immigrants, there was no significant difference between their Korean and English language proficiency. The variable of the immigrant generation was the most significant variable to the language use of Korean Americans due to the uniqueness of Korean American society where different generations are still residing closely and where there is still active inflow of first-generation immigrants from Korea to the US. This phenomenon is unlike other Korean residents in China and the CIS and will be a positive evidence of maintaining Korean in the USA. (Yonsei University)