Objective:To investigate the correlation between the expression level of serum exosome miR-29C and postoperative cognitive dysfunction (POCD) in elderly patients undergoing surgery.Methods:A total of 119 elderly patients who underwent elective spinal surgery in the Second Hospital of Shanxi Medical University from January 2021 to January 2022 were selected and scored on the Montreal Cognitive Assessment (MoCA) Scale 1 day before surgery and 1, 7 and 21 days after surgery. The selected patients were divided into POCD group (51 cases) and non-POCD group (68 cases) according to whether the MoCA Scale score decreased ≥2 points 1 day before surgery and 1 day after surgery. S100-β, neuron-specific enolase (NSE) levels and serum exosome miR-29C expression levels were detected and analyzed in all patients 1 day before and 1 day after surgery. Pearson correlation analysis showed the correlation between MoCA Scale score and S100-β, NSE and miR-29C. Receiver operating characteristic (ROC) curve was used to evaluate the predictive value of S100-β, NSE and miR-29C for POCD occurrence in elderly patients undergoing surgery.Results:The score of MoCA Scale in POCD group were significantly decreased 1, 7 and 21 days after surgery compared with 1 day before surgery (all P<0.05), while the score of MoCA Scale in non-POCD group were significantly decreased only 1 day after surgery compared with 1 day before surgery ( P<0.05). The levels of S100-β and NSE and the expression level of serum exosome miR-29C in 2 groups were significantly increased 1 day after surgery compared with 1 day before surgery (all P<0.05). Moreover, the levels of S100-β and NSE and the expression level of serum exosome miR-29C in POCD group were significantly higher than those in non-POCD group 1 day after surgery (all P<0.05). There was a negative correlation between the MoCA Scale score and the expression level of serum exosome miR-29C 1 day after surgery in the POCD group ( P<0.05). ROC curve analysis showed that the expression levels of NSE, S100-β and exosome miR-29C 1 day after surgery predicted the risk of POCD in elderly surgical patients with area under the curve (AUC) of 0.891, 0.908 and 0.918, respectively. Conclusions:The occurrence of POCD in elderly patients with surgery is related to the increase of the expression level of serum exosome miR-29C, and the expression level of serum exosome miR-29C is negatively correlated with MoCA Scale score. Early monitoring of the miR-29C expression level can provide a basis for the occurrence and development of postoperative POCD in elderly patients, disease diagnosis and clinical intervention.