This paper reports the findings of an action research that was carried out to measure the effectiveness of integrating a social networking website "Edmodo" in students' writing performance in an EFL classroom at Arab Open University (Oman Branch). The participants were 25 students studying English in the Foundation Programme. Along with three lesson plans that were used to teach students the writing process, students conducted some quizzes, discussions and activities on Edmodo. Analysis of students' second writing showed a statistically significant improvement in students' writing. A post-treatment questionnaire results indicated that students have positive perceptions towards using Edmodo in language learning.