The present study examined the roles of different dimensions of syntactic skills in predicting reading comprehension within and across two languages with contrasting structural properties: Chinese and English. A total of 413 young Cantonese-English bilingual students in Hong Kong (202 first graders and 211 third graders) were tested on word order skill, morphosyntactic skill, and reading comprehension in both L1 and L2. Hierarchical regressions showed that after partialing out the effects of age, nonverbal intelligence, working memory, oral vocabulary, and word reading, word order skill was more predictive of reading comprehension in both L1 and L2 in grade 1 than morphosyntactic skill. In grade 3, morphosyntactic skill emerged to be an equally and even a more important skill than word order skill in L1 and L2 reading, respectively. In both age cohorts, L1 syntactic skills cross-linguistically predicted L2 reading comprehension even when age, oral language, and general cognitive skills were statistically controlled. Statistical equation modeling mediation analyses revealed that this syntactic transfer from L1 to L2 was mediated by L2 syntactic skills but not L1 reading comprehension. When we further investigated the transfer of individual syntactic skills, word order skill appeared to be more transferable than morphosyntactic skill early in grade 1, in support of the transfer facilitation model. The findings suggest that young bilingual students may draw on the correspondence between L1 and L2 syntax to support their L2 learning, hence informing educators of issues and strategies that they should take note of in designing an effective L2 learning program.