Mild cognitive impairment (MCI), as a nosological entity referring to elderly people with MCI but without dementia, was proposed as a warning signal of dementia occurrence and a novel therapeutic target. MCI clinical criteria and diagnostic procedure from the MCI Working Group of the European Alzheimer's Disease Consortium (EADC) may better reflect the heterogeneity of MCI syndrome. Beijing United Study Group on MCI funded by the Capital Foundation of Medical Developments (CFMD) proposed the guiding principles of clinical research on MCI. The diagnostic methods include clinical, neuropsychological, functional, neuroimaging and genetic measures. The diagnostic procedure includes three stages. Firstly, MCI syndrome must be defined, which should correspond to: (1) cognitive complaints coming from the patients or their families; (2) reporting of a relative decline in cognitive functioning during the past year by the patient or informant; (3) cognitive disorders evidenced by clinical evaluation; (4) activities of daily living preserved and complex instrumental functions either intact or minimally impaired; and (5) absence of dementia. Secondly, subtypes of MCI have to be recognized as amnestic MCI (aMCI), single non-memory MCI (snmMCI) and multiple-domains MCI (mdMCI). Finally, the subtype causes could be identified commonly as Alzheimer disease (AD), vascular dementia (VaD), and other degenerative diseases such as frontal-temporal dementia (FTD), Lewy body disease (LBD), semantic dementia (SM), as well as trauma, infection, toxicity and nutrition deficiency. The recommended special tests include serum vitamin B12 and folic acid, plasma insulin, insulin-degrading enzyme, Abeta40, Abeta42, inflammatory factors. Computed tomography (or preferentially magnetic resonance imaging, when available) is mandatory. As measurable therapeutic outcomes, the primary outcome should be the probability of progression to dementia, the secondary outcomes should be cognition and function, and the supplement outcome should be the syndrome defined by traditional Chinese medicine. And for APOE epsilon4 carrier, influence of the carrier status on progression rate to dementia and the effect of treatment should be evaluated.