The purpose of this study was to examine the extent to which children's executive function predicted their reading comprehension performance. Participants were approximately 18,000 kindergartners in the Early Childhood Longitudinal Study, Kindergarten Class of 2010-2011. The results suggest that individual differences in reading comprehension were influenced by variations in executive function. Cognitive flexibility, inhibitory control, and working memory all accounted for unique variance in reading comprehension. Language comprehension and fluency mediated the relations between children's executive function and their reading comprehension. Working memory accounted for the highest total effect among the three core aspects of executive function. Children's first-grade language comprehension contributed the most indirect effect, while fluency had the reading comprehension. The importance of considering ways to improve executive function, language comprehension, and fluency when implementing reading instruction and what the parents can do to help their children's executive function and reading skills are discussed.