Background: Studies have shown that word dictation and syntactic skills are significant predictors of written composition performance among Chinese children in elementary grades. However, there is a paucity of research on the bidirectional relationships between these two cognitive‐linguistic skills (i.e., word dictation and syntactic skills) and Chinese writing skills. Methods: This paper reports the findings of a 1‐year longitudinal study tracking the developmental patterns of Chinese writing among students in Grades 3 and 5 in Hong Kong. The participants were administered tasks involving cognitive‐linguistic skills (working memory, word dictation and syntactic skills) and writing skills (narrative writing and expository writing). Results: Multiple regression analysis revealed that word dictation and syntactic skills in Grades 3 and 5 were significant longitudinal predictors of Chinese written composition performance in Grade 4 and Grade 6. Syntactic skills, but not word dictation, contributed a significant amount of unique variance to writing performance after controlling for the autoregressor effect of writing. The results also showed that written composition performance in Grades 3 and 5 contributed unique variance to individual differences in syntactic skills in Grades 4 and 6, after controlling for syntactic skills in the preceding year and other cognitive‐linguistic variables. Conclusion: The patterns of results underscore the significance of syntactic skills in Chinese written composition in upper elementary grades and the bidirectional relationship between syntactic skills and written composition in Chinese. Highlights: What is already known about this topicChinese word dictation, syntactic skills and verbal working memory are the major types of developmental skills important in Chinese writing among children in elementary grades. What this paper addsThe longitudinal contribution of word dictation to writing performance across grades was mediated by the contribution