This paper investigates the code-mixing phenomena and the patterns for code-mixing among a group of trilingual Cantonese-English-Mandarin Post-80s speakers in Macau. Bilingual Cantonese-English code-mixing has been a common phenomenon in the society for decades. Since the handover of sovereignty of Macau to Mainland China in 1999, the use of Mandarin in Macau has become more prominent in the society, especially among the Post-80s as they are the witnesses of the changes after the handover, resulting in an ever-increasing number of trilingual Cantonese-English-Mandarin speakers. This paper aims to explore the Macau trilingual code-mixing patterns and the motivations for these patterns. Data were collected via audiotaping and observing the informal daily conversations among four Post-80s speakers in Macau, as well as by interviewing these informants. The results show that the individual’s language proficiency, language dominance, and the speaker’s perception of her interlocutors’ language background are the three key factors influencing the code-mixing patterns. Trilingual code-mixing occurs not only due to participants’ intention to fill up lexical gaps, but it is also influenced by the social communication trends, such as joking and using trendy expressions. English acts as a popular embedded language and the most useful L2 in Hong Kong and Macau (Chan, 1993, Young, 2006). Although patterns of Cantonese-English and Cantonese-Mandarin code-mixing indicate that the two different language-pairs play different functions, and the latter pattern does not have an impact as strong as that of Cantonese-English code-mixing in the society, English is no longer the one and only one embedded language among the speakers. They are happy to apply Mandarin in daily code-mixing utterances. Mandarin is no more a negative language icon among the locals. These findings are discovered when iii the local Post-80s’s code-mixing behavior with Cantonese, English and Mandarin is investigated in this study. And the result also shows that the generation raises the everincreasing usage of Mandarin in Macau after 1999.