Alzheimer’s disease (AD) is a neurodegenerative disease characterized by extracellular amyloid beta (Aβ) deposition and intracellular neurofibrillary tangle formation. Monocyte is part of the innate immune system and can effectively remove dead cells and debris. It has been suggested that Aβ can recruit monocytes into brain in AD mice, resulting in restriction of cerebral amyloidosis. However, monocyte may act as a double-edged sword, either beneficial (eg, clearance of Aβ) or detrimental (eg, secretion of neurotoxic factors). In addition, recent studies indicate that in AD patients, Aβ phagocytosis by monocytes is ineffective. The present review mainly summarized the current knowledge on monocytes and their potential roles in AD.