Analysis of the China Family Panel Studies (CFPS) data reveals that fertility motivations mediate the impact of internet use on fertility intentions. This mediating role operates in two directions. First, internet use diminishes family-oriented fertility motivations, including family legacy and economic utility motivation, suppressing fertility intentions. Second, internet use enhances individual-oriented fertility motivations, particularly emotion-driven motivation, promoting fertility intentions. Overall, the inhibiting role played by fertility motivation is more pronounced in the influence of internet use on fertility intentions. The mediating effect accounts for 11.251% of the total effect. Further, the impact of internet use on fertility motivation differs across cohorts, genders, urban-rural residences, and education levels. The impacts of different online behaviors on fertility motivation are also different. Exploring the mediating role of fertility motivation contributes to a deeper understanding of the mechanisms through which internet use influences fertility intentions, offering novel insights for addressing low fertility rates in the internet era.