Vocabulary mastery is a basic skill that is needed by students in learning English. Teaching vocabulary involves more than teaching the definition of technical or unfamiliar words in text. In teaching vocabulary, special attention must be given not only to single word but also to some word. The objectives of the research are (1) to know what are the teacher’s strategies in improving students’ vocabulary at SMA Muhammadiyah 3 Yogyakarta, and (2) to know what are the problems faced by teachers’ in improving students’ vocabulary at SMA Muhammadiyah 3 Yogyakarta. The researcher used qualitative research design. To answer the research question, the researcher conducted interview to three respondents of English teachers of SMA Muhammadiyah 3 Yogyakarta and then the researcher analyzed the data by using coding. The findings of this research showed that the teachers had strategies in improving students’ vocabulary. The strategies include giving illustration on how to write and to pronounce the words, reminding and asking the students to repeat, teaching with the context, asking the students to read text book, encouraging the students to practice in the class, encouraging the students to read and talk at home, teaching the important words, encourage students to use dictionary, encourage students to memorize. Asking the students to listen and sing English song, and asking the students to use multimedia. Related to the problems faced by the teacher in improving students’ vocabulary at SMA Muhammadiyah 3 Yogyakarta, the problems faced by the teachers were the students often forget new words, the students lack in reading habit, pronunciation, and spelling,