The study purposes to describe the language shift of Mandailing Language in Mandailingnese family in Medan-Medan Johor. To reach the purpose, this study was conducted by quantitave research. The sample of this study is the Mandailing people live in Medan. The language shift of Mandailing language is investigated through the language use of Mandailingnese families in Medan especially in Medan Johor district Kelurahan Gedung Johor. In collecting the data, the method used to analyze the data is a list of structured questions to obtain information from a number of respondents. The result of the study indicated that there is language shift in teenager and adult level. In teenagers level there were 32% sample who used Mandailing language in their family and in adults level there were 44 % who used Mandailing language in family. On the contrary, in parents level there were no language shift in family, the percentage of the calculation is more than 50% so, there is no language shift in parents level.