Vocabulary is a fundamental factor in learning English. The aim of this research was to improve students’ vocabulary in the fifth grade of SD N 2 Trikarso, Kebumen. The problem was students face difficulties in remembering English vocabulary that they had learnt. Besides that the teacher also rarely uses media in the teaching activities. To solve the problem, the researcher was used pop-up book as media to learn English vocabulary in the learning activities. The method that was used in this research was experimental research. The participants were 21 students of fifth grade of SD N 2 Trikarso, Kebumen. In this research the researcher gave pre-tests to know the participants’ vocabulary mastery before using pop-up book. After that, the researcher applied the pop-up book in the learning activities. It was conducted for three times. Then, the researcher gave post-tests to the participants in order to know the effect of using pop-up book to the students’ vocabulary mastery. Based on the analysis of the pre-test scores’, the students’ vocabulary mastery of fifth grade was in low level, the score was 47.3. Then, the researcher compared it with the students’ post-test scores. The result showed that students’ vocabulary mastery had increased. The mean of post-tests scores were 85.4. It could be concluded that the use of pop-up book was effective to improve students’ vocabulary mastery, so the hypothesis alternative was accepted because it showed that there was a significant effect of the use of pop-up book to improve students’ vocabulary mastery and hypothesis null was rejected.