Error analysis in using modal auxiliaries of the XI Grade Students SMA IT Al-Husnayain Panyabungan Mandailing Natal

The research is focussed on students error in usingmodal auxiliaries. The problem of this research is difficulty to understand the forms of modal auxiliaries for Indonesian learners, because Indonesian language does not have modality to express ability, possibility, probability, and so on. The reasons why students made error in usingmodal auxiliaries are because lack of vocabulary, less attention during process of learning, and less understanding in using modal auxiliaries. There were two purposes of the research, the first is to know what are students’ errors in using modal auxiliaries, the second is to know what are English teacher’ effforts to overcome students’ errors in using modal auxiliaries. This research was conducted through mixed method. Source of data from this research are 36 students from SMA IT A-Husnayain Panyabungan in class XI-2 IPA and English teacher of class XI-2 IPA. The instrument of of this research was modal auxiliaries test and interview. Based on the result of this research, researcher found that error made by students in using modal auxiliaries were omission, addition, misformation, and misordeing. The number of omission error was 25 items error. The number of addition was 13 items error. The number of misformation error was 13 items error. The number of misordering was 78 items error. Total all of the error were 129 item error. Researcher concluded that dominant error made by students in modal auxiliaries use was in misordering category with the percentage 61.90%. From the result of interview, there were three English teacher’s efforts to overcome students error in using modal auxiliaries.Teacher reexplain the material and make an example from the students’ daily activity, teacher asked students to memorize the modal auxiliaries, using media as internet for helping students