This thesis is entitled Improving Students’ Vocabulary by Using Crossword Puzzle (A Classroom Action Research at the Seventh Grade Students of MTs Al Muttaqin in the Academic Year of 2018/2019). Seventh grade A Students have a problem in vocabulary. The purpose of this research was to solve the students’ problem in improving their vocabulary. This research was held in July until August 2018 in MTs Al Muttaqin Rengging. This research was Classroom action research. There were two cycles and one pre-cycle in this research. In the pre-cycle the researcher gave a pre-test to students in order to check their vocabulary mastery before the implementation of crossword puzzle. The score result of the pre-test was 52,7. In the cycle one, the researcher implemented crossword puzzle in learning vocabulary and checked students’ achievement by giving a test. The score result was 61,1. Next in cycle two, the researcher implemented crossword puzzle again in learning vocabulary, but in different way. Then test was given to the students. The result was 73,4. The findings shown that there was improvement score from pre-test 52,7, cycle one test 61,1, and cycle two test 73,4. It means the use of crossword puzzle could improve the students’ vocabulary.