Drawing from Darvin and Norton's (2015) investment model, this study investigates ethnic Tibetan students' multilingual practice and its influence on these students' ethnic identity construction at an interior university in People's Republic of China (PRC). Based on multiple data sources, findings from this study indicate that Tibetan students used specific multilingual semiotic resources from Tibetan, Mandarin, and English languages in constructing their ethnic identities in the interior university. On one hand, Tibetan language is both passive in developing their membership as legitimate Mandarin speakers and critical in their English language learning. On the other hand, they experienced different language negotiation moments in multilingual and monolingual spaces, which further impact on their investment in language learning. Discussions and implications center on these students' different investment in multilingual practices in both academic and non-academic settings and their negotiations of (re)becoming ethnic Tibetans. Implications are provided regarding alternative pedagogies that aim at recognizing the situatedness of Tibetan students' multilingual resources in constructing their ethnic identity.