Tsou people is minority on the ragged edge. This study investigated Tsou language use and language ability by sociolinguistic methods. In the result, well known process of vanishing language were uncovered for Tsou language usage. 1) borrowing words, 2) incomplete bilingual, 3) the language cann't be handed down from generation to generation, and 4) unbalanced bilingual community and language competition. According to Fishman's Graded Intergenerational Disruption Scale, Tsou language has been given the most crisis level which only old people can speak the language. Therefore, these are urgency that mother language education for young adults, and upgrade of Tsuo language to official language.