Objective Cardiac surgery associated acute kidney injury (CS-AKI) strongly correlated with postoperative morbidity and mortality, especially in pediatric population. The purpose of this study was to investigate the role of plasma gelsolin (pGSN) in patients ≤3 years old, and determine whether pGSN was associated with the occurrence and severity of CS-AKI. Methods 77 patients ≤3 years of age performed on cardiac surgery were enrolled. Plasma gelsolin, creatinine, cystatin C and total protein were measured at 7 perioperative time points. Results Normalized pGSN (pGSNN) of AKI group dropped immediately after CPB (p=0.029), and still remained at lower level at 48 hours after CPB (p=0.036); PGSNN of AKI group at 2 hours after CPB was significantly lower than that of non-AKI group (p=0.002). The earliest increase of normalized pCys C (pCys CN) in AKI patients was 24 hours after CPB (p=0.008); PCys CN of AKI group at 24 hours after CPB was much higher than that of non-AKI group (p=0.002). PGSNN at 2 hours CPB was the only independent predictor of CS-AKI (p=0.032), and negatively correlated with the severity of CS-AKI (r=-0.488, p=0.002). Conclusions This study suggested that CS-AKI patients underwent a rapid and persistent drop of pGSNN after surgery; Compared with pCys CN, pGSNN appeared to be a more sensitive predictor of CS-AKI in infant and young children; PGSNN at 2 hours CPB was the only independent predictor of CS-AKI, and negatively correlated with the severity of CS-AKI.