This study aims to advance our understanding of the role of word knowledge in second language (L2) reading comprehension by exploring whether morphological awareness and vocabulary assessed one year ago contribute to decoding and listening comprehension which in turn contribute to reading comprehension in Chinese children learning English as an L2. A total of 167 Grade 3 and 4 primary school students (Mage = 8.99 years) in Hong Kong were tested on English morphological awareness and vocabulary at Time 1, and they were also tested on English decoding, listening comprehension, and reading comprehension at Time 2, one year later. Our regression models showed that word knowledge tested at Time 1 was a significant predictor of decoding, listening comprehension, and reading comprehension at Time 2; and word knowledge explained more variance in decoding, listening comprehension, and reading comprehension in children who had higher levels of word knowledge. The results of structural equation modeling indicated that vocabulary contributed to reading comprehension fully through decoding and listening comprehension. Morphological awareness contributed to reading comprehension partially through vocabulary and decoding, and it also had a unique direct contribution to reading comprehension. The findings from this study suggested the importance of emphasizing word knowledge in developing children’s reading comprehension in an L2 at an early stage of learning to read. Copyright © 2022 The Author(s), under exclusive licence to Springer Nature B.V.