In order to provide the "guiding principles of clinical research on mild cognitive impairment (MCI) (protocol)" edited by Beijing United Study Group on MCI of the Capital Foundation of Medical Developments (CFMD) with evidence support, clinical criteria, subtypes, inclusion and exclusion of MCI, and use of rating scales were reviewed. The authors suggested that MCI clinical criteria and new diagnosis procedure from the MCI Working Group of the European Alzheimer's disease Consortium (EADC) may better reflect the heterogeneity of MCI syndrome. Diagnostic rating scales including Clinical Dementia Rating (CDR), Global Deterioration Scale (GDS), Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog) and Instrumental Activities of Daily Living (IADL) are very useful in definition of MCI but can not replace its clinical criteria. Absence of major repercussions on daily life in patients with MCI was emphasized, but the patients may have minimal impairment in complex IADL. According to their previous research, the authors concluded that highly recommendable neuropsychological scales with cut-off scores in the screening of MCI cases should include Mini-Mental State Examination (MMSE), logistic memory test such as Delayed Story Recall (DSR), executive function test such as Clock Draw Test (CDT), language test such as Verbal Category Fluency Test (VCFT), etc. And finally, the detection of biological and neuroimaging changes, including atrophy in hippocampus or medial temporal lobe in patients with MCI, was introduced.