This research is quantitative research. The research design used was quasi experimental. The subjects in this research were 30 students from class IX' as the experimental class and 30 students from class IX' as the control class. Tests are used as a data collection tool. Data were analyzed using paired sample t- test with a significance level of p < 0.05. The research results show that the vocabulary mastery of students taught without using a guessing game in third prades at SMP Negeri 4 Siabu is 54.80, it was categorized as "less" level. While the vocabulary mastery of students taught by using a guessing game in third grades at SMP Negeri 4 Siabu is 80.13, it was categorized as "good" level. In addition, there is a significant difference in students' vocabulary mastery through the use of guessing game. It can be concluded that a guessing game can improve students' vocabulary mastery.