The title compound, C₁₄H₂₅N₃O₂, consists of a five-membered heterocyclic ring to which a pendant decyl group is attached. The oximino tautomeric character of the molecule is clearly defined by the distribution of well defined double bonds in the heterocycle region (one C=O and two C=N). The most conspicuous packing interaction is the strong intermolecular hydrogen bond linking the oximino OH group and the carbonyl O atom to define broad planar hydrophilic strips running along the unique b axis. The alkyl chains adopt a fully extended conformation and lie almost at right angles to these one-dimensional structures, defining their hydrophobic counterpart.