This study aims to examine the relationship between children’s mean length of utterance(MLU) and their mothers’ language input in bi-cultural families. To begin with, the study presents the findings of an analysis of mean length of the bi-cultural children’s, which is the barometer of their languag development. the children of Chinese mother exhibit very low scores and that the children of Vietnamese mother is similar to those of Korean families in terms of the scales. On the other hand, the mean length of mothers’ utterances is categorized into two: the mean length of bi-cultural mothers and that of native-korean mother, and the result indicates that the mean length of bi-cultural mothers is relatively lower compared to that of their Korean counterparts. To my surprise the mean length of Vietnamese mother stays low whereas that of their children turns out to be higher. The cause of this phenomenon can be traced back to the features and the types of Korean-language utterance in addition to the mean length of mothers’ utterance. The findings reveal that the type of Vietnamese mother’ utterance is characterized by question types designed to facilitate language development, which is similar to the cases of native-korean mother. This implies that the development of children’s language skills have much to do with various factors such as types of question, types of utterance and the length of utterance. (Keimyung University)