Blended learning has become an emerging trend in the field of education and has caught the attention and interest of many researchers as a new approach to encourage students in their learning process, especially during COVID-19 disruption. Blended learning is also known as 'hybrid learning', 'mixed-learning or 'flipped learning' in the literature. The purpose of this study was to investigate the effect of blended learning for improving EFL students', from the eleventh grade, English writing skills and the student's perception of the blended learning environment at a high school. In this study, a mixed-research method was used. The quantitative data was collected through an online questionnaire, pre-test, and post-test writing scores written by 92 participants, and the qualitative data was gathered through semi-structured interviews with 8 volunteer participants. Data were analyzed with SPSS t-tests and content analyses. The research findings showed that blended learning had a significant effect in improving participants' writing skills. Participants significantly outperformed in writing exams. The participants had a positive attitude and perspective towards using blended learning in EFL classes. The limitations of blended learning highlighted by the minority of the participants were the burden of the online activities and lack of internet or mobile device accessibility. Further research on Research Article blended learning models in EFL classes in the K-12 context is highly recommended.