This study aims to explore (1) How is the implementation of metacognitive strategies on teaching writing skill at SMPN 3 Karanganyar? (2) What challenges are encountered in the implementation metacognitive strategies in teaching writing skill at SMPN 3 Karanganyar? This research uses a descriptive qualitative approach with a case study design. The data sources of this research are students, teacher, and the process of writing skill. The study collects data using questionnaires, interviews, observations, and documents. This research uses triangulation data to increase the validity data. The technique of analysing the data that used is interactive model, which consists of data collection, data condensation, data display, and conclusion. The results showed that the implementation of metacognitive strategies in writing skill can be developed and modified by adjusting the learning context and participants. During the implementation of metacognitive strategies in writing skill, time management appears as the main problem faced by both teachers and students. This is due to the implementation of 'P5', which cuts English learning time. This study concludes that the implementation of metacognitive strategies in writing skills can be developed and modified, such as using peer assessment checklists as adding materials that help to guide students in implementing metacognitive strategies in writing. The modification aims to implement MS effectively in which students know their learning plan, know the aspects of monitoring, and know how to evaluating their learning. It is modified by adjusting the context where the research participants were eight-grade students in junior high school. Time management also needs to be considered as the main problem in the implementation of metacognitive strategies. The research is expected to contribute to developing effective learning strategies in the future.