Edmodo is a social learning network and discussion platform where teachers and students can interact and collaborate online. The objectives of this research are to investigate if there is a significant difference in writing achievement between the students who are taught by using Edmodo Website and those who are not taught by using Edmodo Website at Syiah Kuala University. It was also aimed at finding out the students’ response toward the use of Edmodo Website in learning English Writing on Analytical Exposition text. The participants of this research were the fourth semester students of writing class at Syiah Kuala University Banda Aceh. This research used the quantitative method with pre-test and post-test design under the quasi-experimental design. Therefore, the participants of this study were not selected randomly. The participants of this research were 32 students of the fourth semester students to Undergraduate English Department at Syiah Kuala University. The data were collected through test and questionnaire. The collected data from pre-test and post-test were analyzed through a quantitative procedure using the statistical formula to find out the result from experimental class. The researcher identified the data from the students’ assesment in doing analytical exposition text based on these topic; the war in Palestine, a vegetarian diet, mobile phone on society, the dangerous of smoking, being fat matters, and the important of library from both pre-test and post- test. Furthermore, the result of questionnaire from the experimental class was analyzed based on the percentage of the students’ response. The finding of the research shows that the significant differences between the pretest and posttest score. The mean of pre-test scores was 69.06, while the mean of post-test scores was 82.19. The gained score is 13.13. Moreover, the analysis of t-test showed that ttest>ttable (16.476 > 1.697) at the level of significance 0.05 with the degree of freedom (dk) 31. It indicated that the Edmodo Website can improve the students’ writing skill in term organization, content, grammar, mechanics, style and quality of expression.