This study looks at the syllable onset interval (SOI) patterning in Taiwan Mandarin spontaneous speech and its relationship to discourse and syntactic units. Monologs were elicited by asking readers to tell stories depicted in comic strips and were transcribed and segmented into Discourse Segment Units (Grosz & Sidner, 1986), clauses, and phrases. Results showed that the degree of final lengthening was modulated by boundary types. Lengthening before discourse boundaries was longer than that before clausal boundaries, which was in turn longer than that before phrasal boundaries. Final SOI lengthening also seemed to reflect cognitive load. At the discourse and clausal levels, the degree of lengthening is modulated by narration order. First narrations tended to have longer final SOIs than second narrations. In addition, there was also a mild lengthening effect in nonfinal SOIs, as was evidenced by the length differences in initial and medial SOIs and the differential lengthening effect regarding the positioning of phrases in a clause.