The objective of the study is to find out the effectiveness of using Instagram to improve student’s descriptive writing ability at the tenth grade students of SMA N 1 Wedung in the academic year of 2020/2021. The methodology of this research was Experimental Research. The population of this research was all of students at the tenth grade of SMA N 1 Wedung. From the entire population, two classes were chosen as the samples. X MIPA1class was the experimental group and X MIPA 2 was the control group. The technique of data collection was pre-test and post-test to find out the student’s mastery on writing skill, especially in Descriptive Text by using Instagram. The result of this research shows that (1) the result of students before and after treatment were different, (2) there is effectiveness of using Instagram to improve student’s descriptive writing ability because the t-test result of post-test was 3,19 with df was 68 from (na+nb-2) in significant level of 5% and t-table was 1,66. It showed that t-test was higher than t-table (3,19 > 1,66). Based on the finding result of this study, the researcher concluded that there was effectiveness of using Instagram to improve student’s descriptive writing ability at the tenth grade students of SMA N 1 Wedung in the academic year of 2020/2021.

Key Words: Writing, Descriptive Text, Instagram.