This longitudinal inquiry explored the contribution of morphological awareness to English as a Second Language (ESL) reading comprehension. Young Chinese-speaking ESL learners completed twice with a one-year interval the same set of tasks that measured derivational awareness, vocabulary breadth, fluency of reading derived words, and passage comprehension. Structural Equation Modeling analyses disclosed that at both Time 1 and Time 2, morphological awareness had a significant direct impact on reading comprehension over and above vocabulary knowledge, and such an impact became stronger over time. A significant indirect effect of morphological awareness on reading comprehension was also perceived at both times. However, how the indirect effect was attained varied across times. Longitudinally, Time 1 morphological awareness failed to significantly forecast Time 2 reading comprehension over and above Time 1 reading comprehension and vocabulary knowledge; however, an indirect effect via the latter two variables was significant. This inquiry points out an increasingly notable role of morphology in ESL reading comprehension, and a need of explicit teaching of morphology to ease ESL learners’ reading development.