Emerging evidence suggests that executive function plays an important role in adult readers' understanding of text. This study examined the contribution of executive function to comprehension of expository science text among adult readers, as well as the role of vocabulary ability in the relation between executive function and text comprehension. The roles of additional reader characteristics, including age, reading time, prior knowledge, and vocabulary ability, in comprehension were also examined. Using structural equation modeling, a latent executive function factor significantly predicted comprehension after accounting for age, reading time, prior knowledge, and vocabulary ability. Vocabulary ability mediated the relation between executive function and both lower-level and higher-level reading comprehension. Executive function contributed more strongly to lower-level compared with higher-level comprehension of the text. Implications for future research are discussed.