This study examined whether syntactic awareness was related to reading comprehension difficulties in either first language (L1) Chinese or second language (L2) English, or both, among Hong Kong Chinese-English bilingual children. Parallel L1 and L2 metalinguistic and reading measures, including syntactic word-order, morphological awareness, phonological awareness, vocabulary, word reading, reading comprehension, and cognitive measures of nonverbal intelligence and working memory, were administered to 224 fourth-graders. Five groups of comprehenders were identified using a regression approach: (1) 12 poor in Chinese-only (PC); (2) 18 poor in English-only (PE); (3) six poor in both Chinese and English (PB); (4) 14 average in both Chinese and English (AB); and (5) seven good in both (GB). The results of multivariate analyses of covariance showed that: (1) the PB group performed worse than the AB and GB groups in both L1 Chinese and L2 English syntactic awareness; (2) the PC and PE groups performed worse than the AB and GB groups in Chinese syntactic awareness; (3) the PE group had lower performance than the PC, AB, and GB groups in English syntactic awareness; and (4) no significant group difference was found in L2 morphological awareness or vocabulary across both languages. By suggesting that weakness in syntactic awareness can serve as a universal indicator for identifying poor comprehenders in either or both L1 Chinese and L2 English among Hong Kong Chinese-English bilingual children, these findings demonstrate the fundamental role of syntactic awareness in bilingual reading comprehension.