Objective: This study aimed to investigate the clinical value of the left atrial stiffness index (LASI) in evaluating left atrial function in patients with different stages of chronic kidney disease (CKD). Methods: A total of 104 CKD patients admitted to our hospital were included in this study. They were divided into two groups based on estimated glomerular filtration rate (eGFR): CKD1 group (eGFR 30-89 ml·min-1, n=52) and CKD2 group (eGFR <30 ml·min-1, n=52). Additionally, 52 healthy adults undergoing regular physical examinations during the same period were selected as the control group. The differences in general characteristics, laboratory parameters, conventional echocardiographic parameters, and left atrial strain parameters were compared among the groups. The correlation between LASI and cardiac biomarkers (cardiac troponin T [cTnT], myoglobin [Myo], N-terminal pro-brain natriuretic peptide [NT-proBNP]), as well as renal function parameters (serum creatinine [Scr], Urea, cystatin C [Cys-C], eGFR), were analyzed. Multiple linear regression analysis was performed to identify the influencing factors of LASI. Intra-observer and inter-observer reproducibility of ultrasound parameters (LASr, LAScd, LASct, LAD) were assessed using the intraclass correlation coefficient (ICC). Results: The levels of cTnT, Myo, NT-proBNP, Scr, Urea, Cys-C, and LASI increased gradually, while eGFR decreased gradually in the control group, CKD1 group, and CKD2 group, with statistically significant differences observed among all groups (all P<0.05). LASI showed a good correlation with NT-proBNP (r=0.601, P<0.001) and eGFR (r=-0.577, P<0.001). Multiple linear regression analysis indicated that NT-proBNP was an independent influencing factor for LASI in CKD patients. The reproducibility analysis demonstrated good intra-observer and inter-observer reliability of left atrial ultrasound parameters (intra-observer ICC: LASr=0.992, LAScd=0.98, LASct=0.984, LAD=0.982; inter-observer ICC: LASr=0.995, LAScd=0.996, LASct=0.989, LAD=0.99). Conclusion: LASI can serve as an effective index for evaluating left atrial function in patients with different stages of CKD, with its value increasing as CKD progresses.