Writing assessment to monitor students progress in writing skill is often implemented in English as a Forign Language (EFL) classroom. The assessment should be adhered with the principles of second language assessment. One of principles is washback. Washback is an effect of assessment. Washback in assessment generally refers to the effect of test in teaching and learning in terms of students preparation. It means that washback can occur before the assessment.This research aims to find out the activities students do in regard with writing assessment and the washback of writing assessment. This research used qualitative research design and interview was used as the data collection method. The researcher interviewed four students batch 2017 at English Language Education Deapartment (ELED) of a private university in Yogyakarta. The result showed that writing assessment presented positive washback. Students perceived three positive washback of writing assessment that was conducted in ELED. First, the assessment makes students do some preparation. Second, feedback gives benefit for students writing ability. Third,the result of assessment makes students study the material.