Sri Endang Feo Pengarang Tans Feliks Dosen Pembimbing 1 Gupuh Rahayu Dosen Pembimbing 2 Fransiskus Bustan Ketua Penguji Tans Feliks Penguji 1 Gupuh Rahayu Penguji 2

This research aims to find out how Extensive Reading technique improves students’ vocabulary mastery at grade X of SMK KENCANA SAKTI HAUMENI. The research wanted to find how the extensive reading improve students vocabulary mastery, this research conducted Classroom Action Research. The subjects of the study were 21 students of X (Upw) C of SMK KENCANA SAKTI HAUMENI . The technique of analyzing the data of this research was applied by quantitative and qualitative data. The quantitative data were taken from the students’ test that pre-test and post-test . The qualitative data were taken from the students’ score, interview sheet, test, and observation sheet. There are two meetings during the research conducted pre-test and post-test. The implementation of Extensive Reading in this research is by asking the students to read English story for 10-15 minutes in every meeting. The results showed that Extensive Reading can improve students’ vocabulary mastery based on the increasing in students’ vocabulary mastery and the changes in students’ behavior. It was found out by measuring the mean scoreof the tests result. The improvement was also shown from the reflection of Cycle1 and Cycle 2. It is shown that the students know much new vocabulary. In addition, the activities made the students more enthusiastic in teaching and learning process. Therefore, Extensive Reading can improve students’ vocabulary mastery by the way of reading, exercising in vocabulary assignment more and more, and working in groups .