ABSTRACT The aim of my study is to investigate the role of code-switching constituents in Chinese/Portuguese discourse in Macao and to try to determine the nature of the grammatical rules which govern their occurrences. This study utilizes data collected from tape-recorded interviews of a group of seven Chinese/Portuguese bilingual men and women. A set of questions was prepared, the context of which was predicted to obtain occurrences of code-switching. With this data, I examined 1) the number of code-switching occurrences; 2) the kind of code-switches that the informants used; 3) the grammatical constraints are applicable to all of our data. The results of this study indicate that intrasentential code-switching is the most common type of code-switching found in the data, with the noun being the most commonly code-switched item. I also found that there are grammatical constraints which govern Cantonese/Portuguese code-switching in Macao and which govern the limits of where a bilingual speaker can code-switch.