HERWANTO Pengarang Sastika Seli, S.Pd., M.A. Dosen Pembimbing 1 Dewi Syafitri, M.Pd. Dosen Pembimbing 2 Maria Ramasari, M.Pd. Penguji 1 Sastika Seli, S.Pd., M.A. Ketua Penguji Dr. Hamdan, M.Pd. Penguji 2 Herwanto Contributor

This research aimed to find out whether or not it was significantly effective to Applying Duolingo Application to Improve the Students’ Vocabulary Mastery in Writing Skill at SMPIT An-nida’ Lubuklinggau. The method applied was Pre-experimental method with one group pre-test and post-test design. The Population was all of the eighth grade students of SMPIT An-nida’ Lubuklinggau which consist of 95 students. The sample was taken by using cluster random sampling. The number of the sample were 20 students. Before the treatments, the researcher gave the pre-test to the students. Then, after the treatment the researcher gave the post-test to the students. The data were analyzed through three technique, they were: (1) individual score, (2) conversion of individual score, (3) matched t-test. Based on the result of the data analysis, there were three major findings, 1) The mean score in the pre-test, it was 56.35; 2) the means score in post-test was 78.57; and 3) the result of matched t-test calculation showed t-obtained was 8.75, which t table was higher 1.729. Therefore the alternative hypotheses (Ha) was accepted and null hypotheses was rejected. It means that it was significantly effective to Applying Duolingo Application to Improve the Students’ Vocabulary Mastery in Writing Skill at SMPIT An-nida’ Lubuklinggau. Keywords: Applying, Duolingo Application, Writing Skill