The concept of mild cognitive impairment (MCI) is clinical condition between normal cognition and dementia. Annual rate of conversion from MCI to dementia is estimated as 10-15%. It must be emphasized that all MCI will not be potential patients of dementing illness. Most studies have been focused on amnestic-MCI as preclinical condition of Alzheimer's disease (AD). Along with the increase number of analyses, MCI is divided in four categories according to clinical presentation such as amnestic-MCI, amnestic-MCI with multiple domains, non amnestic-MCI with single domain and non amnestic-MCI with multiple domains. In general, the underlying disease of amnestic-MCI with multiple domains may be AD, cerebrovascular disorders (CVDs), metabolic disease or depression. Non amnestic-MCI may be frontotemporal dementia, dementia with Lewy body, CVDs and metabolic disorders. In fact, neuropathologic evidence of MCI revealed the presence of various types of pathologic change. Those pathologic changes include an accumulation of tau, amyloid beta, α-synuclein, TDP-43 and FUS protein with various degrees. It is not unusual condition that several different types of pathology are observed in a single individual. Besides neurodegenerative pathology, CVDs and hippocampus sclerosis significantly contribute the cognitive condition of MCI. To realize the complexity of neuropathologic alterations of MCI is important for early intervention of dementia indivisuals.