This article examines the current use of the ethnic language of the Thai and Muong students at Thanh Hoa ethnic minority high boarding-school in comparison with their use of the national language (Vietnamese) as well as the level of change in language influenced by urbanization and modernization. The research points out that the Muong people in Thanh Hoa province have a large population living on the urban edge and in remote rural areas where the terrain is favorable to communication and exchange with the outside world. One result of this has led to an increased fluency in speaking Vietnamese than the residing Thai population. However, the languages of the Thai and the Muong people in general and those of the students of such the two ethnic minorities in particular are in accordance with the common trend of a changing use of language in Vietnam today. Currently, ethnic minority languages in Vietnam are gradually diminishing in favor of the national language. This change reflects hegemony of cultural exchanges between the ethnic majority and the ethnic minorities as well as rapid rate of modernization occurring across all regions in Vietnam.