Journal of English Language Learning (JELL), Vol. 6 No 2, 142-148 ISSN 2599-1019 Page | 142 The Effect of Using Duolingo Application Towards Students’ Vocabulary Mastery at the Eighth Grade of SMPN 2 Banjarsari Lebak-Banten Puput Permatasari 1 , Ade Sudirman 2 , Tatu Munawaroh 3 1,2,3 English EducationDepartment, University of Mathla’ul Anwar , Banten, Indonesia *e-mail: puputpermatasari69@email.com Abstract: The purpose of this research was to find out the emperical evidence of The Effect of Using Duolingo Application Toward Students’ Vocabulary Mastery at The Eighth Grade of SMPN 2 Banjarsari Lebak-Banten In Acaddemic Year 2021/2022. In this research, the quantitative methode was used and the research design was a quasi-experimental. To conduct the research, 76 students of eighth grade student of SMPN 2 Banjarsari Lebak academic year of 2021/2022 are choosen as the sample in this research. They were VIII A class as the experimental class, and VIII B class as the control class. Each class consisted of 25 students. This number was taken as the sample of this research by using Mr.Excel and SPSS 25. Duolingo application was used as an instrument in the experimental class while the control class uses the Hello English Application. Based on the calculation, the post-test mean scores of the experimental class was 70.12 while that of the control class was 59.36. The researcher got the result from testing with SPSS 25 t-test obtained the t-count =6.301in control class and signification value (p-value)=0.000 < a =0.05, and with t-test obtained the t-count= 6.463 in experimental class and significant value (p-value) =0.000 < a = 0.05 Ha is accepted and Ho is rejected. The result indicated that using Duolingo is effect towards students’ vocabulary mastery and had a moderate effect at the eighth grade of students SMPN 2 Banjarsari Lebak in the acaddemic year of 2021/2022. Keyword: Duolingo, Application & Vocabulary mastery INTRODUCTION Language is important in human life because, without language, human beings will not able to do anything (Ibda, 2019). Language is needed in this modern life, to communicate with other countries (Anggraini, 2016). In Indonesia, English is the first foreign language that became the subject at school that should be learned by students in formal education from the lowest to the highest level and it also examined in the national examination (Hamied, 2012; Lie, 2007; Sulistiyo, 2016). In teaching and learning activities, English has four language skills to learn; those are listening, speaking, reading, and writing (Bailey, 2003; Banditvilai, 2016; Bozorgian, 2012; Khamkhien, 2010). The most important English learning component is comprehending the vocabulary (Anjomshoa & Zamanian, 2014; Jun Zhang & Bin Anual, 2008). vocabulary is the prior element in English that the students need to comprehend and it should be taught to them because it has a key role in every language in the whole world, in which without vocabulary we can not understand each other. According to Handayani (Kusumawati, 2018) vocabulary is knowledge of words and meanings. Based on the statement, vocabulary is all the words in a language..that are familiar and used by someone to communicate..with each other. Vocabulary is a major concern in junior high school materials because vocabulary is a collection of several words that are combined, meaning or meaning. Successful communication or saying what you mean is dependent upon a good vocabulary base. Vocabulary is an important point in learning a language because it is the main part to begin our listening, speaking, reading, and writing (Pikulski & Templeton, 2004). Vocabulary is not a simple matter, because learning thousand of words make the students bored. Nowadays, people have been living in the globalization era, in which the development of technology grows rapidly. Eventually, they try to find a lot of information by using the internet. They browse much information and news through the internet. The growth of technology is related to the development of English. Technology can change the method of people work, learn, interact, and spend their time. Along