This study concerns the codes and their frequencies used by Ambonese students of Petra Christian University in certain domains: friendship, daily life, education, and religion domain. The data were taken from a structured interview, which is based on a questionnaire given to forty Ambonese students in Petra Christian University. All the respondents were interviewed one by one by the writer based on the questions in the questionnaire. Furthermore, this study is supported by Sociolinguistic theories of codes and domain of language use presented by Janet Holmes. Finally, the writer found out that the Ambonese students tend to use the Indonesian language in formal domains, like education and religion. Besides, Ambonese as their mother tongue was mostly used in the friendship domain while talking about something informal. While, the use of Suroboyoan as the variety used by the majority people in Surabaya, often used by students in Petra Christian University, was used when the Ambonese talk or interact casually with their friends from Surabaya. Furthermore, since the interaction of Ambonese students in PCU are not limited only to those from the same ethnic group, but with others from other ethnic groups, the use of Kupangnesse, Papuans, English, and Jakarta dialect are also applied in certain domains