Abstract: Objective To investigate the monitoring of renal microcirculation perfusion alteration with contrast-enhanced ultrasound(CEU) during cardiopulmonary bypass(CPB). Methods Renal microcirculation perfusion before and during CPB was assessed by CEU. Time-intensity curve (TIC) were derived from three region of interest (ROI) using QLAB post-analysis software. Parameters such as TIC curve wash in slope (A), area under curve (AUC), peak intensity (DPI) as well as time to peak intensity (TTP) were then calculated. Results Contrast-enhanced ultrasound showed a significant reduction (or elongation) of perfusion parameter (A, AUC, DPI,TTP) in all three regions (superficial cortex, deep cortex and medulla) during cardiopulmonary bypass in comparison with normal cardiac cycle. Conclusion Cardiopulmonary bypass (CPB) has a dramatic impact on renal microcirculation in pediatric patients which manifest as global reduction in renal perfusion as well as significant region perfusion difference. Contrast-enhanced ultrasound (CEU) could detect the renal microcirculation alteration during CPB.