Coastal students' tense on grammar really affects their grammar mastery. Mostly the factors of the tense are neither from their relationship, environment, nor personal matters. It is from their perception on grammar itself. The purposes of this study are (1) to identify the stressors; (2) to describe the impacts of the stressors on grammar ability. The method used was descriptive quantitative. The setting of the research was in one of the universities in Tanjungpinang, Riau Archipelago, Indonesia. The population of this research was the second semester students comprising 78 students in the academic year of 2018/2019. Questionnaire and grammar test were used to collect the data, and it was analyzed by using Rasch Model. This study revealed (1) from the 30 items of the questionnaire about the students' tense in academic and non-academic factors, only two items were the dominant stressors i.e. having grammar difficulties and facing grammar examinations and they were from the academic factors; (2) Those whose stress was high on grammar difficulties i.e. 29 (37.18%) students showed bad performance at grammar tenses but interestingly those whose stress was high on grammar difficulties i.e 17 (21.79%) students also had good performance at grammar tenses. There were 1 (1.28%) and 15 (19.23%) students who claimed that the grammar difficulties never and rarely stressed her or him but s/he went bad performance at grammar tenses. In fact, those whose claimed that the grammar difficulties rarely made them stressed had good performance at grammar tenses i.e. 16 (20.51%) students. Then, those whose stress was high on facing grammar examination i.e. 32 (41.03%) students had bad ability at grammar tenses. In contrary, those whose stress is high on facing grammar examination i.e. 17 (21.79%) students had also good performance at grammar tenses. The other students claimed that facing grammar examination rarely stressed her or him i.e. 1 (1.28%) got bad performance at grammar tenses; the other 2 (2.56%) students made good performance at grammar tenses. Facing grammar examination, 12 (15.38%) students who never stressed showed bad performance at grammar tenses and the other 14 (17.95%) students went good performance at grammar tenses. Therefore, students' tense on grammar tense(s) is the matter of perception which should be changed for better grammar mastery.