Using Chinese listed companies from 2011 to 2023 as a sample, this study examines the bilateral spillover effects of focal firms’ data assetization on upstream and downstream innovation, as well as the underlying mechanisms. The results show that data assetization of focal firms stimulates innovation among both upstream suppliers and downstream customers, but the spillover effects are asymmetric, with a stronger impact on downstream customers. Mechanism analysis reveals that these effects operate through information and knowledge spillovers. Specifically, supplier innovation is mainly enhanced via information spillover, while customer innovation is primarily driven by knowledge spillover. In addition, the innovation spillover effects of focal firms’ data assetization become more significant when geographical distance is shorter and relational distance is greater.