The research was intended to increase the students’ vocabulary mastery in SMAN 1 Ngaglik by utilizing Wordwall as learning media throughout teaching and learning. It was classroom action research, which was conducted in three cycles among the tenth-grade students of Social 3 class. In each cycle, the research covered the stages of reconnaissance, planning, implementation, observation, and reflection. The data were collected using qualitative and quantitative approaches. The qualitative data were gathered by observing teaching and learning processes, interviewing collaborators and students, and taking photographs. Meanwhile, the quantitative data were obtained by assessing students' knowledge through pre-tests and post-tests. The results revealed that applying Wordwall successfully improved the students' vocabulary mastery, which was shown in the class average score which reached 83.72. The success was achieved by incorporating the use of English as a medium of instruction, actively engaging students in knowledge-building, employing guessing games, and providing feedback and rewards.