This study aims to study factors affecting level of Korean language proficiency for North Korean Refugee Adolescents dwelling in Korea. 30 North Korean Refugee Adolescents were asked to answer three different questionnaires designated to investigate Korean language proficiency, Acculturative Stress and demographic background. This study adopts altered TOPIK for the evaluation of Korean language proficiency, and focuses on finding out the relationship of Korean language proficiency with sexuality, age, years of Korean study, and duration of dwelling in China. The SPSS for windows 15 was used for the statistical analysis. Acculturative Stress Scale was measured with the ASIS that was developed by Sandhuand Asrabadi(1994) and Proficiency Test that was selected by TOPIK (Test of Proficiency in Korea) session 22, 23. Cronbach for Acculturative Stress Scale was 0.898. Internal consistency reliability for Korean proficiency test was 0.897. The result shows that learning methods(Korean friends or books), duration of stay in China, Korean use, learning period, age, and gender have significant relationship with level of Korean proficiency, especially periods living in China has more significant relationship with the proficiency. The result from this study helps to recognize factors affecting level of Korean language proficiency. Specifically, the Korean proficiency of North Korean Refugee Adolescents who live in Korea has a close relationship with Acculturative Stress Scale. These facts indicate that not only the Korean education are required to effectively increase the Korean education itself, but also developing the competency of Cultural Acculturation are needed to be followed up as well for North Korean Mission.