Aldehyde dehydrogenase 1 family member A3 (ALDH1A3), also known as retinaldehyde dehydrogenase 3 (RALDH3), is a member of the aldehyde dehydrogenase family known to metabolize a wide variety of aldehydes. ALDH1A3 specifically oxidizes retinal to retinoic acid (RA) and is differentially expressed in developing embryonic tissues and adult organs. The RA produced by ALDH1A3 in rodents contributes to the development of skin and hair follicles, brain, tooth buds, lungs, olfactory bulbs, kidneys, eyes, skeletal muscle and seminal vesicles. In recent research, ALDH1A3 could be as a marker of cancer stem cell to predict metastasis or clinical prognosis in many cancers.