This study describes teachers’ competence in understanding curriculum and its impact on English instructional quality. The choice for the topic is because it is quite important to find out the impact of teachers’ competence in understanding curriculum on instructional quality used for the students. If we can find that out, we might better understand the bigger question of why the government must ensure that all English teachers have a comprehensive understanding of the current curriculum: by creating avenues to enhance their (teachers) effective communication/ socialization skills, regular and evenly -providing engaging workshop or training for the teachers whose understanding competence must improve for better instructional quality, to be imparted to the students. So, to be able to advise the government and just anyone that better instructional quality can improve understanding on the part of the students, structured interviews were used to collect the data of this qualitative research. The data collected from 15 English teachers at 6 Senior high schools in Pidie (Indonesia) were analysed using descriptive statistics. This research found that the students’ achievement of Minimum Completeness Criteria was still low due to the English teachers’ low understanding of the curriculum in preparing the teaching process, doing pedagogical teaching activities, and implementing teaching evaluation. These findings contribute not only to helping educationists carry out further related research but also to the government ensuring that the implemented curriculum runs well.