This research aimed to describe: (1) the kinds of language instructions used by lecturers in EAP classrooms, (2) the aspects of language instructions used by lecturers in EAP classrooms, (3) the students? responses towards the use of language instructions.
This research was conducted at UPT Bahasa, Universitas Sebelas Maret, Surakarta. The techniques of collecting the data used in this research were observation, interview, document analysis, and questionnaire. The informants consisted of three lecturers and the students of each EAP  classroom  at UPT Bahasa,  Universitas  Sebelas  Maret.  The  documents  were  transcript  of  the lecturers? language instructions during the teaching and learning process, field notes, transcript of the questionnaire, and transcript of the interview.
Based on the analysis of the data, it can be concluded that (1) the dominant languages used by those three lecturers during English teaching and learning process respectively were Indonesian language, English, and Javanese language. (2) In general, the dominant aspects used in English were DP/disciplining pupils, CW/commenting on work, GAI/giving activity instructions, AQ/asking questions, and CIP/chatting informally with pupils. In addition, the dominant aspects used in Indonesian language consisted of SH/setting homework, CM/correcting mistakes, TG/teaching grammar, EM/explaining meaning,  and EL/explaining lesson.  (3) The students could interact with the lecturers when the lecturers used both English and Indonesian language during the teaching and learning process. Therefore, it is recommended for English lecturers to use language instructions properly to make the students understand more about what the lecturers are talking about, to make the students use more English vocabulary, to make the lecturers and the students have an enjoyable and successful English teaching and learning process. For the other  researchers  who  want  to  conduct  a  similar  research,  the  result  of  this research can be an additional reference.