The purpose of this study is to find out the effectiveness of pictorial posters as a medium to encourage vocabulary mastery among seventh-grade students at SMP Negeri 1 Karangmoncol. The research used a quantitative approach using an experimental design. This study used a random sampling technique. The samples were separated into two groups: the experimental group in VII H (32 students) and the control group in VII G (32 students). Data collection began with pretest questions administered before the treatment, followed by treatment in the experimental class utilizing pictorial poster media, while the control class did not receive any media. Following the treatment, the students took a posttest to compare the results before and after the treatment. The T-test result yielded a significance value of 0.000, indicating that the alternative hypothesis (Ha) was accepted and the null hypothesis (H0) was rejected. Furthermore, the N-Gain analysis found a difference in average scores, with the experimental group achieving 59.81% and the control group only reaching 17.19%. Based on the effectiveness scale, the experimental class can be considered fairly effective in terms of N-Gain. This suggests that the use of Pictorial Posters effectively enhances students' vocabulary mastery.