ABSTRACT
This research aims are (1) to find out whether the use of animation video can improve vocabulary mastery of the studetns. (2) to describe what happens when animation video is implemented in English class to improve students’ vocabulary mastery at the fifth grade students of SD Negeri Purworejo 35 Surakarta.    
The method used in this research is a classroom action research which was conducted in two cycles. Qualitative data were collected using observation, interview and diary, while quantitative data were collected using test. The qualitative data were analyzed through assembling the data, coding the data, comparing the data, building interpretation, reporting the outcomes. The quantitative data were analyzed by comparing the mean score of the pre-test and the post-test.
The research findings showed that (1) the implementation of animation video can improve students’vocabulary mastery. It can be seen from the students’ mean score from 3.30 in the pre-test which improves into 6.95 in post-test 1 and 7.71 in post-test (2) the use of animation video gives positive effect in the classroom situation. It is indicated by: the students looked more enthusiastic in teaching learning process; the students also became active and confident in answering the researcher’s task or question. The classroom situation also became more conducive..

Keywords: Animation Video, Vocabulary Mastery, Class Action Research