<p>Extreme precipitation intensifies under global warming, yet its impact on sea-air CO₂ flux (FCO₂) remains underexplored. Here we show that the maximum 1-day precipitation (Rx1day) exerts a notable influence on FCO₂ in the South Pacific Ocean and South Atlantic Ocean during 1990–2023. An increase in Rx1day from 0 to 30 mm causes the South Pacific Ocean and South Atlantic Ocean to shift from carbon sources to carbon sinks, with FCO₂ decreasing from 96 to −27 mmol&#xa0;m⁻²&#xa0;month⁻¹ and from 70 to −70 mmol&#xa0;m⁻²&#xa0;month⁻¹, respectively. This reduction is likely attributed to precipitation-induced dilution effects on salinity and alkalinity. When precipitation increases by up to 20%, FCO₂ exhibits maximum reductions of 27% (5.6 mmol&#xa0;m⁻²&#xa0;month⁻¹) in the South Pacific Ocean and 10% (6.4 mmol&#xa0;m⁻²&#xa0;month⁻¹) in the South Atlantic Ocean. Neglecting precipitation may result in a non-negligible overestimation of FCO₂, underscoring the necessity of incorporating it into ocean carbon budget models.</p>