Alzheimer's disease (AD) is the most common neurodegenerative disease and the leading cause of dementia worldwide. Different pathologic changes have been introduced to be involved in its progression. Although amyloid-β (Aβ) deposition and tau hyperphosphorylation and aggregation are mainly considered the main characterizations of AD, several other processes are involved. In recent years, several other changes, including alterations in gut microbiota proportion and circadian rhythms, have been noticed due to their role in AD progression. However, the exact mechanism indicating the association between circadian rhythms and gut microbiota abundance has not been investigated yet. This paper aims to review the role of gut microbiota and circadian rhythm in AD pathophysiology and introduces a hypothesis to explain their association.