Objective:To observe the functional remodeling of the default mode network (DMN) of patients with post-stroke cognitive impairment (PSCI) in response to transcranial direct current stimulation (tDCS) and to explore the mechanisms involved.Methods:Eighteen PSCI patients and twenty healthy controls were enrolled. The PSCI patients were given 20 minutes of tDCS at 2.0mA on the dorsolateral prefrontal cortex every weekday for four weeks. The subjects were scanned using resting state functional magnetic resonance imaging before and after the intervention to explore any functional changes in the DMN. Montreal cognitive assessment (MoCA) scoring was performed before and after the treatment.Results:Compared to the healthy controls, the cognitively impaired patients showed significant abnormalities in the DMN on admission, including decreased functinal connection (FC) in the posterior cingulate cortex and/or precuneus (PCC/PCu), as well as increased FC in the medial prefrontal cortex (MPFC) and left hippocampus. After the treatment, a significant improvement in the PSCI patients′ average MoCA score was observed. The average FC of the PCC/PCu had also increased significantly, while that of the left hippocampus had decreased significantly, on average. The FC in the PCC/PCu after tDCS was found to be positively related to the MoCA score measured at 4 weeks after admission.Conclusions:PSCI patients show functional abnormalities in the DMN. tDCS applied to their dorsolateral prefrontal cortex can significantly improve their average MoCA scores, which may be related to the increasing FC of the PCC/PCu.