Recent advances in microbial pathogen research have highlighted the potential of gut microbe-based microbial medicine. One of the most extensively studied biological pathways is the gut-brain axis, which has been shown to reverse neurological disorders. Evidence from animal-based studies of dysbiosis suggest complex behavioral changes, such as alterations in sociability and anxiety, can be modulated through gut microbiota. Specifically, mental disorders include major depression, bipolar disorder, and schizophrenia. Gastrointestinal diseases can be reversed by modulating gut microbiota. Dementia and its related mechanisms are also amenable to modulation of the gut microbiota. This review focuses on the role of gut microbiota in dementia by discussing the effects on depressive symptoms, cognitive function, mood, behavioral changes, chronic stress, and the prospects of the microbiota-gut-brain axis for dementia. Although animal models have revealed promising approaches for treating dementia through the modulation of the gut microbiota, it may be premature to incorporate these interventions into standard clinical practice. The heterogeneity of findings from clinical trials and randomized control trials has yet to convincingly demonstrate the efficacy of modulation in reversing dementia and its related complications.