The third tone sandhi in Mandarin is a well-studied rule, where a Tone 3 followed by another Tone 3 is changed as a rising tone, similar to Tone 2. This Tone 3 sandhi rule is straightforward in disyllabic words, which is phonetically driven for the ease of production. In three or more than three syllables with Tone 3, however, the Tone 3 sandhi application is more complicated and involves both the prosodic and morph-syntactic domains, which makes it difficult for L2 learners. This study aims to understand how L2 learners with another tone language experience could master the Mandarin Tone 3 sandhi rule. Specifically, the study investigates the production of Tone 3 sandhi in trisyllabic Mandarin words by Cantonese speakers. In the current study, 30 Cantonese speakers were requested to produce 15 trisyllabic words (“1+[2+3]” and “[1+2]+3” sandhi patterns) and 5 hexasyllabic sentences with Tone 3 in sequences. The analyses of results center on three major types of error patterns: overgeneralization, under application, and combination. The findings are discussed with regard to the phono-syntactic interactions of Tone 3 sandhi at the lexical and phrasal levels as well as the influence of the Cantonese tonal system.