Formaldehyde is a useful ingredient for wood preservatives and resin products, but because it is a causative agent of sick house syndrome, it has attracted attention. Shampoos, skin lotion, and foundation products used in everyday life are generally called cosmetics, and the ingredients used in them are subject to particularly strict regulation because they are applied to the human body. Japan’s Standards for Cosmetics (Ministry of Health and Welfare Notification No. 331, 2000) list formaldehyde as one material which is prohibited to include in cosmetics. Moreover, in the EU, the content of formaldehyde in nail polish and other nail products is limited to no more than 5%. In this article, formaldehyde in cosmetics was detected using the HPLC method and the post-column derivatization with acetylacetone, which is an established test method under the Methods of Analysis in Health Science (The Pharmaceutical Society of Japan, 2015). This article introduces examples of analysis of formaldehyde using a Nexera™ Series Nexera XR ultra high performance liquid chromatograph.