It is a practical and urgent issue to understand linguistic problems of multicultural students. The actual conditions of Korean use by international marriage children was surveyed in this study, because the proportion of international marriage children is high among multicultural children. To elucidate the linguistic problems of international marriage children, mentors for them were interviewed and their diary were analysed. The linguistic problems of international marriage children are occurred when they learn Korean through their mother, a marriage immigrant who is not proficient in Korean. The pronunciation of international marriage children does not cause public problem, when they become elementary school students. The pronunciation of international marriage children during daily conversation is not at issue comparing to that of usual students. However, reading and writing ability of international marriage children is low comparing to that of usual students. The international marriage children are not good at the differentiation of “/æ/” from “/e/”, palatalization, and pronunciation of diphthong. By the analysis of their dictation ability and their diary, it was found that they are not proficient in differentiating morpheme and they write words according to pronunciation. They are not fluent in conceptual words and abstract words. Also they are absolutely lacking in the amount of vocabulary. They cause emotional problems, because they are not familiar with refined expression. They usually do not refine their emotion, and then express their emotion directly. Therefore it is necessary to teach them in consideration of their self-respect, home background, friend relationship, and brotherhood relationship. The results of this study on the linguistic problems of multicultural students will be a guide to selection of contents for the development of teaching materials for multicultural students.