The effects of transcription skills, comprising both spelling and handwriting fluency, on sentence writing among young Chinese as a second language (CSL) learners were evaluated and compared to those of reading and oral language using a one-year longitudinal study design. Various writing models postulated that transcription skills are essential in early writing development; however, studies have not yet clarified its role in CSL writing alongside other important writing component skills such as reading and oral skills. Participants included 204 primary-school-level CSL learners. These learners were evaluated in copying, spelling, character reading, oral language skills, and sentence writing at the end of the Grades 4 and 5 school year. Regression and path analysis evaluated the direct and indirect effects of the component skills on sentence writing. The results showed that, while controlling for non-verbal reasoning, (1) Time-1 transcription skills predicted sentence writing concurrently and longitudinally, but their influences at Time 2 diminished considerably for the substantial autoregressive effect of writing; (2) character reading predicted sentence writing both at Times 1 and 2, and contributed to spelling development; and (3) compared with transcription and reading, oral language skills weakly influenced writing, which was mediated largely by character reading. The findings suggest that transcription skills are vital constituents of CSL sentence writing and that reading plays a primary role in the reading-writing relationship in this stage.