Directive feedback is one of strategy to check students' grammatical error in writing. This strategy is used by the lecturer in PETA (Principle of Effective Teaching and Assessment) course during third semester. This research used case study to investigate whether directive feedback could improve students' writing skill. Besides that, it also tried to explore the commonest grammatical error in student's writing and students' feeling toward directive feedback. The participants of this research were students of Universitas Siswa Bangsa Internasional, who took PETA course. The data was gained from record observation and students' interview. Record observation was obtained from students' reflection during PETA course. The result was directive feedbacks could improve students' writing skill with one condition. That is students should be aware of the feedbacks given by the lecturer and learn it. The conclusion opens possibility for further research to find the level of effectiveness of directive feedback in improving students' writing skill and the level of students' writing skill improvement.