Objective: To investigate the influence of inhaling different concentration of sevoflurane on post-operative cognitive dysfunction (POCD) in the elderly patients and evaluate the correlation between serum of homocysteine(Hcy) and POCD. Methods: Sixty ASA Ⅰ~Ⅱ patients undergoing lower gastrectomy were randomly assigned to two groups,group A inhaling low concentration of sevoflurane (n = 30) and group B inhaling high concentration of sevoflurane (n = 30). After the induction of anesthesia,1.5% sevoflurane (group A) or 3.0% sevoflurane (group B) were given for anesthetic maintenance. The mimi-mental state examination (MMSE) was used to assess the cognitive function before and 6,24,72 h after the operation. The serum Hcy before and 2 h in the operation and 24,72 h after the operation were determined. Results: The difference of MMSE scores between two groups before the operation were insignificant (P > 0.05). Compared with the preoperative values,MMSE scores were significantly reduced at 6 h in two groups(P < 0.05),which is lower in group B than group A(P < 0.05). Compared with the preoperative values,the serum Hcy at 2 h in the operation and 24,72 h after the operation in group A increased insignificantly(P > 0.05), while the serum Hcy at 2 h in the operation in group B increased significantly (P < 0.05),and returned to baseline at 24,72 h after the operation(P > 0.05). Conclusion: Inhaling high concentration of sevoflurane was easier to result in POCD than inhaling low concentration of sevoflurane. Serum Hcy level was related to the concentration of inhaling sevoflurane.