Vol 3 No 1 (2023) : SoCul:International Journal of Research in Social Cultural Issue 750 THE USE OF DUOLINGO APPLICATION TO INCREASE STUDENTS’ VOCABULARY MASTERY Kristyanti A. Borang 1 , Mister G. Maru 2 , Rinny Rorimpandey 3 English Education Department, Faculty of Language and Arts Universitas Negeri Manado, Tondano, Indonesia Email: kristyantiadhelheidb@gmail.com Abstract : The objective of this study is to find out if the Duolingo Application could aid students to improve their vocabulary mastery especially adjective. This research was conducted in quantitative method with pre-test and post-test design through a written test. The subject of this study were 31 students from SMP Negeri 1 Manganitu class 8 B. According to the data obtained, the mean Pre-Test score is 43,32, with the greatest Pre-Test score is 83 and the lowest is 10, and the highest Post-Test score is 97 and the lowest is 63, and the Post-Test’s average score is 79.80. Significant improvements can be noted in this data, and it can be concluded that the use of Duolingo application successful for increase students’ vocabulary mastery. Keywords : Vocabulary mastery, Duolingo Application, English Learning INTRODUCTION Humans are social beings who need to interact with each other. In the process of interaction, humans need language to communicate with each other. Language is a tool to express ideas, information, concepts, or feelings that emerge from the heart , (Salipadang et al., 2021). Among the several languages spoken in different nations, English is an international language and the language most widely used by mankind in this world. In Indonesia, English is one of the foreign languages studied at various levels of education. This is based on realizing the importance of mastering English to face the current era of globalization. The four skills that are taught in the English language are listening, speaking, writing, and reading. Of course, to learn, all these abilities, it is necessary to have good vocabulary mastery. Students may not fully comprehend the dialogue when listening. They are unable to converse effectively without a sufficient vocabulary. Students may struggle to comprehend the text when reading. Student may find it challenging to express their thoughts in writing (Maru, et al, 2022). It will greatly assist kids in the process of learning English if they have a large vocabulary. It will be difficult for foreigners to understand a new language if they do not acquire the vocabulary of the language. “Since vocabulary affects how successfully speakers, listeners, readers, and writers communicate, it is a crucial component of language ability.” (Richard and Renandya, 2002:255 in Jaelani & Sutai, 2020). Students must study vocabulary in order to improve other language skills, such as speaking, writing, reading, and listening. If pupils are having trouble understanding or comprehending the material they are reading, it is because they are unfamiliar with the meaning of terms. If they only have a few vocabulary words, it will be difficult for them to converse in a new language. Mastering a language is difficult if you do not begin with the easiest, and learning a new language without mastering vocabulary is impossible Because vocabulary plays such an important part in all languages, it is one of the English components or sub-skills that students should be taught. According to to Cameron (2001:73) cited in Zikriyati & Syafei (2018) knowing words is what