Exposure to sevoflurane and other inhalational anesthetics can induce cognitive impairment in elderly patients. Studies have indicated that methylene blue (MB) has beneficial effects on multiple neurodegenerative diseases and the mechanism involves mitochondrial function preservation. However, whether MB can attenuate the cognitive decline induced by sevoflurane in aged mice requires further investigation. Forty-five 18-month-old C57/BL mice were used to establish a model of sevoflurane-induced cognitive impairment in which the mice were exposed to 3% sevoflurane for 2 h. Mice in the MB group were intraperitoneally injected with MB at a dose of 5 mg/kg before sevoflurane inhalation. The Morris water maze test was used to evaluate the learning and memory performances. We also examined changes in mitochondrial morphology as well as the expression and interaction of related proteins in the aged hippocampus. Parkin, BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3), mitochondrial dynamin-related protein 1 (Drp1), small ubiquitin-like modifier (SUMO2/3), SUMO-specific proteases 3 (SENP3), and ubiquitin-like conjugating enzyme 9 expression in the mouse hippocampus was detected by western blotting, and SUMO2/3-Drp1 was examined by coimmunoprecipitation. Exposure to sevoflurane increased SENP3 expression and Drp1 deSUMOylation in the aged hippocampus and resulted in cognitive deficiency. MB attenuated sevoflurane-induced memory loss and mitochondrial fragmentation and decreased Drp1 deSUMOylation in the aged hippocampus. This neuroprotective effect provides a mechanistic explanation for how the SUMOylation status of Drp1 acts as a key switch in the cognitive dysfunction induced by sevoflurane.