This research aims to obtain empirical evidence of the influence of using Documentary Films on students’ writing ability of explanation text. The method of this research was a quantitative method using a quasi-experimental design. The population of this research was the eleventh-grade students at one of the private schools in Tangerang Selatan in the academic year 2019/2020 with 61 pupils in total. The sample of this study was selected by purposive sampling technique and was divided into two classes; experimental class and control class. In collecting data from both classes, the researcher used a written test as an instrument. Moreover, the data from both the pre-test and post-test were analyzed by using a t-test with IBM SPSS 20. The result indicated that the post-test mean score of the experimental class was higher than the post-test mean score of the control class, 76.97 > 67.16. Then the sig. 2-tailed (ρ) was lower than the alpha, 0.000 < 0.05. It proved that H0 was rejected and Ha was accepted. Therefore, the effect size calculation result showed 1.60, which means it is at a strong level. Therefore, it proved that there was a significant influence of using documentary films on students’ writing ability of explanation text.