Word reading and word spelling are important processes of literacy acquisition for children. The longitudinal relationship between reading and spelling is still unclear, especially among bilinguals and biscriptals. In the present study, we compared the longitudinal word reading-spelling relationship in L1 (Chinese) and L2 (English), together with early cognitive-linguistic skills. Participants were 182 pairs of Chinese-English bilingual twins who were tested annually across 3 years on word reading and word spelling in both scripts. Chinese and English cognitive and linguistic skills were measured in the first year only (mean age = 7.38). Cross-lagged panel models were applied to analyze the longitudinal word reading-spelling relations. Predictors of word reading and word spelling differed between Chinese and English. Longitudinally, there were no bidirectional or unidirectional relationships between word reading and spelling in Chinese. In contrast, a reciprocal relationship between word reading and spelling was revealed in English. This study underscores similarities and differences in the development of literacy skills among biscriptal readers of L1 Chinese and L2 English.