An UN Number (United Nations number) is a four-digit number that identifies hazardous materials, and articles (such as explosives, flammable liquids, oxidizers, toxic liquids, etc.) in the framework of international transport. There are around 2500 active UN numbers. Disclaimer Our content is not in any way legal advice or binding. The information provided by might not be the official legal or full definition. Also when pursuing a specific transaction you are encouraged to conduct your own due diligence and to consult legal counsel as appropriate.