Lee Hyun-hee and Park Chul-woo. 2013. The correlation between adult literacy and their vocabularies. The Sociolinguistic Journal of Korea 21(3). The subject of literacy is no longer new, as it is clear that understanding various types of text is essential for daily life. However, it is also true that once adults have completed their formal school education, they are typically not provided with formal opportunities to improve literacy or vocabulary skills. In the context of lifelong learning, this reality opens the need for an exploration of the relationship between adult literacy and vocabulary. This paper discusses the findings from an experiment on adult literacy. Subjects were divided into two groups: Group A consisted of fifty adults over the age of fifty, and Group B consisted of fifty undergraduate students. The main results of this study can be summarized as follows. First, it was found that Group A overestimated their own literacy and vocabulary abilities, while Group B underestimated these skills. Secondly, in terms of the four language skills of speaking, listening, reading, and writing, Group A reported relative ease of use of these language functions. In comparison, Group B responded that they sometimes experienced difficulties in reading and writing. However, on test items pertaining to lexemes, synonyms, content, and genre, the percentage of correct answers from Group A was lower than that of Group B. As a result of this experiment, we can conclude that the actual literacy of Group A was lower than that reported in their self-evaluations. Based on this finding, we suggest the necessity of literacy and vocabulary education for adults. (245 words)