Abstract: Aldehyde dehydrogenase 1A1 (ALDH1A1), one of the 19 aldehyde dehydrogenases, is a very important non-P450 oxidase participating in the second step of vitamin A metabolism. To be specific, it irreversibly oxidizes retinal to retinoic acid to restrain the toxicity of retinal. Moreover, the metabolite, retinoic acid, is also an essential active substance which plays multiple physiological roles by regulating nuclear receptors such as retinoid X receptor (RXR) and retinoic acid receptor (RAR). ALDH1A1, whose expression and activity change under pathological conditions, is involved in the development of metabolic diseases (e.g. obesity and diabetes), psychiatric diseases (e.g. Parkinsonism and Alzheimer's disease), cancers (e.g. lung cancer and breast cancer), etc., and is thus a potential target to treat diseases. This paper summarizes the change and action mechanism of ALDH1A1 in disease progression, its structure and catalytic mechanism, as well as the research progress of its inhibitors.