Objective: This study aimed to investigate the relationship between the changes of serum indoxyl sulfate (IS) concentration, Klotho protein level, and cardiovascular complications in patients with chronic kidney disease (CKD) stage 3-5. Methods: A total of 108 patients with CKD stage 3-5 were selected. They were divided into three groups: CKD stage 3-4 group, CKD stage 5 non-dialysis group, and CKD stage 5 dialysis group. Echocardiography was used to measure left ventricular diameter (LVD), interventricular septal thickness (IVS), left ventricular posterior wall thickness (LVPW), and calcification. Results: there was no significant difference in age between the healthy control group and the patients with CKD stage 3-5 (p > 0.05). Compared to healthy controls, serum creatinine, serum phosphorus, iPTH, serum IS, left ventricular diameter, interventricular septum thickness, left ventricular septal wall thickness, and the proportion of valve calcification increased gradually, while serum calcium and Klotho protein decreased The level of serum IS was positively correlated with the level of LVD, IVS, and valve calcification in CKD patients, while the level of serum Klotho protein was negatively correlated with the level of IVS and valve calcification in CKD patients. Conclusion: In patients with chronic kidney disease (CKD), the incidence of cardiovascular complications is significantly higher than in the general population. The increase of serum IS level and the decrease of serum Klotho protein level are closely related to cardiac injury, it IS suggested that serum IS level and Klotho protein level may be a good index for monitoring cardiovascular injury in CKD patients.