Abstract In Mandarin Chinese, a relative clause (RC) can either immediately precede the head NP, or may be separated from its head by a numeral-classifier sequence (NCL). This word order variation results in two types of indefinite nominal constructions: the OMN with the RC + NCL + NP order (e.g., [tā xiě O de]RC [yī–běn]NCL shū, ‘a book (that) he wrote’) and the IMN with NCL + RC + NP order (e.g., [yī–běn]NCL [tā xiě O de]RC shū, ‘a book (that) he wrote’). In this paper, we use a corpus-linguistic perspective to explore the conditioning factors that influence the variation of these two constructions in discourse. In particular, grammatical roles of relativized NPs; information status, animacy, and discourse salience of head NPs; grounding mechanisms; and discourse functions of relative clauses are analyzed. Examinations of the distribution and occurrence of these two constructions show that they are deployed in discourse to serve different discourse purposes. The OMN is mainly used in connection with abstract entities with low discourse salience, and serves the discourse function of identifying the new head NP. In contrast, the IMN is mainly used in conjunction with concrete (human and concrete object) entities with high discourse salience to serve the discourse function of characterization. It will be argued that the variation of these two constructions can be explained with regard to the cognitive and communicative principles of relevance (Sperber and Wilson, 1995) together with interactions between the discourse function of the NCL and the discourse functions of the RC.