Situation-Bound Utterances (SBUs), as a typical kind of idiomatic expression, have been well studied mainly in English, but to date have been little studied in Mandarin. What are the unique characteristics of Mandarin SBUs? What lies behind this uniqueness? To answer these questions requires uncovering the psychological reality of SBUs among Mandarin speakers and filtering out samples based on a clear definition. In this study, the socio-cognitive approach is taken. This approach synthesizes the advantages of a pragmatic and cognitive view of language communication in which concept and lexicon are viewed as two inter-related but mutually independent entities. SBUs act as an appropriate tangent point to illustrate the relationship between concepts and linguistic forms. Under such a perspective, the study of Mandarin SBUs in this paper will reinforce and complement the cognition of this unique linguistic phenomenon. This paper first defines SBUs according to certain maxims and then demonstrates various kinds of idiomatic expressions in Mandarin and clarifies the relationships among these expressions and SBUs. Thirty samples are filtered out through three approaches: individual reflection, collective contribution and reference consulting. The paper then sets three tests to confirm and reconfirm the selected thirty quasiSBUs. Finally, following a discussion of Mandarin SBUs vis-à-vis linguistic form, language policy and social-cultural factors, conclusions are posited as to why Mandarin SBUs are somewhat different from their English counterparts.