This study investugated on the effect of collaborative writing on students’ achievement as observed from students’ point of view. It used pre – experimental design which organize using factorial design. The data collected the result of pre-test and post test score and the survey of students’ belief on collaborative writing. According to the discussion and research findings in this study, it can be conclude that there is significant effect of writing descriptive text collaboratively on seventh-grade students of I Islamic Junior High School An Nawawiyyah. In other words, they achieve higher score after implementing collaborative writing than before it. Also, mostly learners have positive belief after working collaboratively in writing descriptive text. They think collaborative writing give the effective learning and solve their weakness such as stuck on writing, less vocabulary and understanding correct grammatical term. Yet, several students have negative change after collaborative writing because they find less cooperative partner so that they are also less motivated during writing collaboratively. Therefore, they are not enthusiastic to discuss with their partner. Based on interview with student who is less motivated, they think their idea is better than their partner.