The title compound, C(10)H(24)N(+)·C(8)H(15)O(2) (-), forms a layered structure in which inter-molecular N(+)-H⋯O hydrogen bonds connect anions and cations, forming a two-dimensional network parallel to (010). The n-alkyl chains of the decyl-ammonium cations pack according to an ortho-rhom-bic 'subcell' with approximate dimensions 5.1 × 7.3 Å, and they are significantly distorted from planarity.