In this research, the objective of the study was to find out whether or not documentary films as a media is effective to improve the tenth grade students’ ability in writing report text. This research was categorized as a quasi-experimental research with two groups : experimental group and control group. The subject of this research was 70 students which were taken from two classes of X MIA 1 class as an experimental group and X IS 1 as a control group. The validation this research used face and content validity, for face validity used real teacher to be expert judgmentto validate the test item by using a rubric appearance of test and it is conformity by curriculum as a content validity. This research also uses inter-rater reliability in giving scores to the students’ and for measuring the reliability of the test, this research used SPSS then conducted by Pearson’s correlation formula.The data was collected by using writing test through several activities. They were : pre-test, treatments and post-test.
The result of this study showed that there was improvement on students’ ability in writing report text. It can be seen from the final scores of the experimental group and the control group. The mean score of post-test of the experimental group was 77.15, while the mean score of post-test of the control group was 70.56. And from the result of independent t-test for t-value reached 4.957, then sig. showed 0.000 which it means that 0.000<0.05. This research also successes to gain the score of the students, each class was increased after they got the treatments. The control class was increased 3.21 while in experimental class was 8.06. Therefore, the result indicated that H1 was accepted and H0 was rejected. At the end of the research, it can be concluded that the use of documentary films is effective and can help students to improve their ability in writing report text.

Keywords: Documentary films, report text, teaching writing.