This study aims to find out the reasons the postgraduate students use code-switching in their daily interactions. The method of this research is a qualitative method and a questionnaire on google form is used to collect the data. The result from this research is that the students' code-switch in their daily interaction to make the message much clearer, to keep the interaction going on, and to emphasize the message. to clarify the message, to convince the addressee, to quote something, to involve another party, to show respect, to show social status, and other reasons such as to tell a secret and to improve their English skills, to practice their English, to arouse other people to speak English, to talk about taboos, to talk about ghosts, to use English spontaneously when watching YouTube or having a chit chat with friends, to discuss sensitive topics, to look classy and educated, to adjust to the situation and conditions or the interlocutors, to borrow English words, for euphemism, to comment those who do not come from Indonesia, to communicate their intention easily, to become more confident, too shy to express some feelings or thoughts in the Indonesian language, and to swear.

Keywords : Code-Switching, Postgraduate Students, English as a Second Language, Bilingual.