KAREN NANDITA MIRA Pengarang SELFIANA P MBADI Dosen Pembimbing 2 Alexander Home Kabelen Dosen Pembimbing 1 Alexander Home Kabelen Penguji 1 Novriani Rabeka Manafe Ketua Penguji SELFIANA P MBADI Penguji 2

The research objective was to determine whether or not the Quizlet application is effective for teaching and learning vocabulary for students of SMPN 2 Kupang Timur and the challenges students find in applying the Quizlet application in learning English vocabulary. The research applied quantitative research. The research sample was 40 students of VIII A & B, divided into two groups; one as the experimental group and one as the control group. They were given two tests and a non-test: Pre-test and Post-test, and a close-ended questionnaire. The experimental group used the Quizlet Application. Then they used their mobile phone to access the material on the Quizlet Application, and when they finished the Post-test, they filled the questionnaire. The data was then analyzed using SPSS 16 and descriptive statistical analysis. The result of the research found that the value of t0 (2.382) >tt (2.037) and the importance of significance level of p significance (2-tailed) is (0.23) < (0.05), which means that the use of the Quizlet Application is effective. The research also found some challenges in using the Quizlet Application: the internet connections, the availability of tools (handphone/computer) to access the application. Keywords: Quizlet Application, vocabulary, mastery