Undecanal, also known as undecyl aldehyde, is an organic compound with the chemical formula C10H21CHO. It is an eleven-carbon aldehyde. A colourless, oily liquid, undecanal is a component of perfumes. Although it occurs naturally in citrus oils, it is produced commercially by hydroformylation of decene. It has been registered under the EU REACH scheme at >1000 tonnes by , which confirms the status as irritant.