Objective <p>To determine the relationship between intraoperative decreased renal and cerebral oxygen saturation, as measured using near-infrared spectroscopy (NIRS), and cardiac surgery-associated acute kidney injury (CSA-AKI) in adults.</p> Methods <p>This prospective observational study was conducted at Peking University International Hospital. Between November 2022 to August 2023, 101 adult patients undergoing cardiac surgery under cardiopulmonary bypass were included. Renal and cerebral tissue oxygen saturation was continuously monitored during the operation using NIRS.</p> Results <p>The overall incidence of CSA-AKI was 27% (27/101), with a 4% incidence rate of requiring renal replacement therapy. The incidence of CSA-AKI was 57% (13/23) in patients with renal desaturation compared to 18% (14/78) in those without renal desaturation (<i>P</i> &lt; 0.01). CSA-AKI occurred in 71% (12/17) of patients with cerebral desaturation compared to 18% (15/84) in those without cerebral desaturation (<i>P</i> &lt; 0.01). The incidence of CSA-AKI was 100% (7/7) in patients with simultaneous renal and cerebral desaturation. Renal desaturation alone showed a sensitivity of 48%, while the combination of renal and cerebral desaturation demonstrated 100% specificity for predicting CSA-AKI.</p> Conclusions <p>In adult patients, 27% experience CSA-AKI. Intraoperative renal or cerebral desaturation, as monitored by NIRS, is associated with a higher risk of CSA-AKI, with simultaneous renal and cerebral desaturation which yielded the highest specificity in predicting postoperative AKI.</p> Trial registration <p>This study has been registered on the Chinese Clinical Trial Registry number (ChiCTR2200065161, 30/10/2022).</p>