Reading is an essential part in foreign language learning as the understanding of a written text and vocabulary is one of language elements that can affect students’ reading comprehension. Therefore, this paper tries to describe the importance of having adequate vocabulary to improve students' reading comprehension score of EFL learners in Indonesia. Firstly, this study provides the some strategies that can be used in teaching vocabulary proposed by Brewster, Ellis, and Girard (1992) and reading comprehension summarized by Coe (2009), and then, this paper states the relationship between having mastery in vocabulary and reading comprehension. The present paper concludes that having more adequate vocabulary affects students’ reading comprehension. It is assumed to the students to enrich their vocabulary by practicing to read more which can help them in gaining vocabulary and comprehending the text.