English is a language with numerous words that appear or sound quite similar to one another. These confusing words are one of the most significant obstacles for English learners. It commonly leads the learners to make mistakes because of the similarity of pronunciation, meaning, or spelling with other words.

The researcher employed Classroom Action Research in order to answer the formulated research questions. The participants of this study were students of XI MIPA 2 of SMA Pangudi Luhur Sedayu. To collect the data, the researcher administered pretest and post-test. In addition, the researcher distributed questionnaires to students to determine their perspective on the use of Instagram Video from Discovery English to enhance their vocabulary mastery.

The result indicated that Instagram videos from Discovery English contributed to the student's improved vocabulary mastery. The class's mean score increased from 73.12 to 91.64 after administering the treatment. Moreover, the students showed a positive perception toward using of Instagram videos since numerous benefits were obtained, such as improving vocabulary mastery, enhancing cross-cultural awareness, boosting the power of creation, and increasing their learning motivation.

Keywords: CAR, confusing words, Discovery English, Instagram videos