Abstract: In the context of the strategy of "dual-carbon" target and the high-quality development empowered by fintech, it is of great practical significance to investigate the carbon emission reduction effect of fintech. Utilizing panel data of 284 cities in China from 2011 to 2021, this paper empirically examines the impact of fintech development on urban carbon emissions efficiency and its underlying mechanism. The results show that the fintech development significantly enhances the efficiency of urban carbon emissions, a finding that remains robust after incorporating a one-period lag of financial technology development level, replacing explained variables, and conducting tail trimming. Heterogeneity analysis reveals that the positive effects of fintech on urban carbon emission efficiency are more pronounced in Northeast China, megacities, non-resource-based cities, cities with higher levels of financial development, and non-urban agglomerations. Mediation effect tests further indicate that fintech development boosts the urban carbon emissions efficiency through two pathways: technological innovation and industrial structure upgrading. Consequently, it is recommended to increase support for fintech, consider regional development disparities, implement differentiated fintech-driven emission reduction strategies, strengthen fintech mechanisms, and fully leverage the driving role of fintech to promote the green transformation of cities.