This study aims to study factors affecting level of Korean language proficiency for Korean Missionaries' Kids (MK) dwelling in Turkey. 45 Korean MKs were asked to answer three different questionnaires designated to investigate Korean language proficiency, cultural identity and demographic background. This study adopts altered TOPIK for the evaluation of Korean language proficiency, and focuses on finding out the relationship of Korean proficiency with sexuality, age, age at immigration to Turkey, years of Korean study, self-recognition of cultural identity, cultural identity of Korea, and cultural identity of Turkey. The SPSS for windows 17was used for the statistical analysis.Ethnic Identity Scale was measured with the KAEIS that was developed by Ahn(1999) and Proficiency Test that was selected by TOPIK (Test of Proficiency in Korea) session 19, 20. Cronbach  for cultural identity of Korea was 0.823 and Cronbach  for cultural identity of Turkey was 0.691. Internal consistency reliability for Korean proficiency test was 0.891. The result shows that cultural identity of Korea and age at immigration to Turkey have significant relationship with level of Korean proficiency, especially age at immigration to Turkey has more significant relationship with the proficiency. The result from this study helps to recognize factors affecting level of Korean language proficiency. Especially, the Korean proficiency of MKs who live in Turkey has a close relationship with Korean cultural identity.These facts indicate that not only the Korean education are required to effectively increase the korean education itself, but also developing the pride of being Korean are needed to be followed up as well.