Writing as a type of productive skills has been a major concern, particularly for vocational high school students. Writing is regarded as tough for students in English proficiency courses. As a result, collaborative writing is used to keep students interested in writing. The goals of this study are to discover how a collaborative writing strategy can improve students' writing descriptive texts in eleventh grade. The researcher employed Classroom Action Research (CAR). The researcher went through two cycles of planning, implementing, observing, and reflecting. The data was acquired through quantitative and qualitative methods. The quantitative data were derived from the students' writing scores (preliminary test, cycle I and cycle II test results), while the qualitative data were derived from the interview and observation results. The success criteria for this study need 88% of students to attain or pass a score of 75. The findings of this study indicate that the application of the Collaborative Writing strategy is effective in improving students' writing skills. Students are able to meet the requirements for success by applying brainstorming, conceptualizing, outlining, drafting, reviewing, revising and editing in Collaborative writing activities in class. The total number of students who met the success criteria ranged from 11.5% (preliminary test) to 50% (test results of cycle I) and finally 88.4% in test result of cycle II. Meanwhile, the results of questionnaires and observations revealed that the use of Collaborative Writing techniques provides several benefits for students, including enriching thinking, leading to creative writing, and improving writing skills. Based on these data, the researcher suggests that teachers use this method when teaching writing to encourage students to write better. In addition, students can use this method outside the classroom to develop their writing skills with their peers. Meanwhile, the researcher suggests that future researchers take this work more deeply from a different perspective on learning theory