The title compound, C(4)H(6)N(3)OS(+)·H(2)PO(4) (-), (I), was obtained as a result of hydrolysis of [(1,3-thia-zol-2-yl-amino)-carbon-yl]-phospho-ramidic acid, (II), in water. X-ray analysis has shown that the N-P bond in (II) breaks, leading to the formation of the substituted carbamide (I). This compound exists as an inter-nal salt. The unit cell consists of a urea cation and an anion of H(2)PO(4) (-). Protonation of the N atom of the heterocyclic ring was confirmed by the location of the H atom in a difference Fourier map. The mol-ecules of substituted urea are connected by O⋯O hydrogen bonds into unlimited planes. In turn, those planes are connected to each other via N-H⋯O hydrogen bonds with mol-ecules of phospho-ric acid, forming a three-dimensional polymer.