Vocabulary is an essential part of language, and also a very important element in the process of teaching and learning a language. The vocabulary can help the students to gain success in studying English language skill. However, based on the data that was obtained from the English teacher at grade XI of SMA N 5 Sungai Penuh academic year 2018/2019, it was found that the students did not have much vocabulary in English, because of that they were not interested in learning English. Therefore, the objective of this research is to know the use of mnemonics technique could improve the students’ vocabulary mastery or not at grade XI of SMA N 5 Sungai Penuh. The form of this research was a classroom action research, the action research was conducted to the students at grade at grade XI of SMA N 5 Sungai Penuh academic year 2018/2019. There were 20 students as participants in this research. This classroom action research was conducted in three cycles with four meetings. Each cycle consisted of four steps namely planning, action, observation, and reflection. In collecting the data, the researcher used instruments namely test, observation and field notes. While in analyzing the data, the researcher calculated and analyzed all of data. From the data analysis, the result of test showed that the students’ vocabulary mastery improved from cycle one to cycle three. The mean score of test in cycle one was 48,5% and increased to 63,25% in cycle two, and increased to 70,5% in cycle three. From the mean score, the students improved their vocabulary. There were also positive changes in students’ behavior in learning English. These improvements were caused by some factors. The factors were teaching way, classroom activities, classroom management and motivation. Therefore, it could be concluded that teaching vocabulary using mnemonics technique could improve the students’ vocabulary mastery.
