East Asian countries have experienced rapid demographic changes. Thus far, declining fertility rates and the expansion of higher education for women have been reported in the literature, with contrasting solutions for different policy environments and societal contexts; therefore, nuanced knowledge is needed. We took a comparison approach to analyze cohort changes in the relationship between women's educational attainment and fertility behaviors in China and Japan, employing discrete-time event history models and difference-in-differences (DID) analysis. The results revealed divergent trends in the 2 countries: Japan showed a weakening negative association between higher educational attainment and fertility behaviors over time, whereas China exhibited a persistent trend influenced by historical population control policies. We argue that sociocultural contexts and policy environments play crucial roles in shaping women’s fertility behaviors. To address the demographic challenges associated with unique social conditions, China needs to develop more nuanced policies rather than mirror Japan's policies. Additionally, this research demonstrates how ultralow fertility can emerge without significant shifts in family attitudes or rising individualism, contributing to the broader discourse on the second demographic transition in East Asia.