Objective:To investigate changes of intestinal flora and the mechanism of NLRP3 inflammasome in elderly mice with cognitive dysfunction induced by sevoflurane anesthesia.Methods:Eighteen fourteen-month-old male SPF grade C57BL/6J mice were randomly divided into control and sevoflurane groups, with 9 mice in each group. The mice of sevoflurane group inhaled 3% sevoflurane for 2 hours daily for three days. Fecal samples were collected post-exposure 24 hours for 16S rRNA sequencing. Morris water maze was then used to test the cognitive ability. Western blot was used to detect the expressions of synapse-associated proteins, NLRP3 inflammasome-related proteins of hippocampus, and NLRP3 inflammasome-related proteins of colon. Golgi staining was used to observe the number of dendritic spines in the hippocampus. qPCR was used to detect the expression of inflammatory cytokines IL-1β, IL-18, TNF-α mRNA in mice colon and hippocampal tissues.Results:(1) The Morris water maze test showed that the escape latency of the sevoflurane group was longer than the control group, but there was statistical difference only on the fifth day ( P<0.05). In the spatial exploration test, escape latency of the sevoflurane group was higher than that of the control group((49.50±9.99)s, (18.67±7.63)s, t=6.005, P<0.001), and platform crossing frequency was less than that of the control group((0.83±0.75)times, (2.33±1.03)times, t=2.87, P=0.017). (2) Western blot and Golgi staining results showed that the expression of hippocampal synaptic-related proteins and the number of dendritic spines in the sevoflurane group were significantly reduced compared with those in control group (all P<0.05). (3) 16S rRNA sequencing showed significant β-diversity difference between the two groups ( P<0.05). Compared with the control group, potential pathogens that p_Desulfobacterota and g_Desulfovibrio increased significantly in the sevoflurane group (both P<0.05), and beneficial bacteria that p_Verrucomicrobiota and g_Akkermansia decreased significantly (both P<0.05). (4) Compared with the control group, the results of qPCR showed increased expression of inflammatory cytokines TNF-α, IL-1β mRNA in the colon and hippocampal tissues of the sevoflurane group (all P<0.05). Western blot results showed increased expression of NLRP3 inflammasome-related proteins in the colon and hippocampal tissues of the sevoflurane group (both P<0.05). Immunofluorescence results showed the higher fluorescence intensity of ASC in the DG region of the hippocampus of the sevoflurane group compared with the control group ( P<0.01). Conclusion:The cognitive dysfunction model induced by sevoflurane in elderly mice shows neuroinflammatory reactions and synaptic damage, which may be related to intestinal microbiota imbalance and activation of NLRP3 inflammasome.