This research was inspired by the researcher’s experience doing the third apprenticeship program conducted by the university, when grammatical errors in English writing were an issue in the school. Hence, the purposes of this research are to find out the most frequent types of grammatical errors made by students in English writing and to describe the causes of errors made by students in English writing. The research method used by the researcher was descriptive qualitative approach. The samples involved in this study are
15 students studying in the 2B class of Multimedia study program of SMK Negeri 1 Hulu Gurung, Kapuas Hulu. In particular, the data from writing test of recount text reveals the most frequent type of errors as well as the incorrect grammatical features made by students in writing, while the data from interview focused on the causes of errorsfrom students’ perspective. To analyze the data, researcher use a content analysis to analyze data from writing test (recount text) and thematic analysis from the results of interview.
The result of research from the given writing test showed that, from 15 pieces of English writing submitted, the students wrote 1457 words in total and made 75 sentences with grammatical errors. One of the main findings revealed
that students inaccurately added 22 (13%) grammar units to sentences and omitted 44 (26%) grammatical features that were required to be there, such as punctuation and articles. Another finding showed that the misordering type of
error is the least common one that students make in their English writing, occurring only 9 times (or 5% of the total errors). On the other hand, some students believed that they tended to make grammatical errors in English writing due to the interference of their mother tongue (i.e., Bahasa Indonesia). To sum up, the findings suggest teachers to apply teaching strategies and lessons that promote more exposure to English language and its grammatical rules in order to minimize the interference of mother tongue in writing.

Keywords: Grammatical Errors, English Writing, and First Language Interference