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 Cognitive disorders are one of the major public health issues in older population worldwide. Problems in forming and storing new memories, short-term memory impairment, and other cognitive problems are common symptoms of cognitive disorders that have no definite treatment yet. Recent studies have shown an association between gut microbiota and cognitive impairments described as microbiota-gut-brain axis. It seems that gut microbiota is able to influence behavior, brain system, and cognitive functions through this pathway in old age. In this review, the underlying mechanisms of the effect of gut microbiota on cognitive disorders and the role of dietetic intervention with probiotics in cognitive function are discussed.