Silence as a communicative act in face-to-face spontaneous interaction has been under-investigated in linguistic politeness research in Thailand. With the recent increase in the influx of foreign students gaining admission into Thai universities yearly, the result is that such universities will be a coexistence of cultures. This study therefore aims to investigate the situational face-threat contexts where Thai students use silence as a politeness strategy. This aim is guided by the main research question of what different situational face-threat contexts could lead to the use of silence by Thai students in their foreign-peer interactions in a Thai multicultural university context. Twenty students' interactions were sampled using micro-socio-ethnographic technique, with data from observation, interview, and questionnaire. The main findings revealed that: uncertainty of language proficiency, expected hurting words from interlocutor, and unexpected negative change in hearer's mood, amongst others, were the main circumstances where Thai students use silence as a face-saving politeness strategy. The findings imply better intercultural awareness in multicultural university contexts.