This study is to investigate the effectiveness of using crossword puzzles to improve English vocabulary mastery in the Seventh Grade of SMPN 16 Semarang in the Academic Year 2021/2022. This study used quantitative research method and experimental research design. This sample of the research is 66 seventh grader students of SMPN 16 Semarang. They are from 2 different classes, Students of VII D class as the experimental class, whereas students of VII C as the control class. So, there are 33 students from each group participating. This research used a written test of the pre-test and post-test as the instruments. Based on the independent sample test done for each group, the sig. (2-tailed) of the experimental post-test group is 0.000. since it is less than 0.05. It is found that H0 was rejected and Hα was accepted. It means, there was a significant effect of using crossword puzzles on enhancing students' English vocabulary mastery.