The thermal decomposition of pyridinium (PyH) and imidazolium (ImH) hexavanadates, (PyH)2V6O16 . H2O and (ImH)2V6O16 . H2O, was studied by dynamic methods. The decomposition is influenced by the properties of the cation. PyH, which is thermally more stable, gives rise to the (PyH)HV6O16 intermediate at 275-degrees-C which is then decomposed at 420-degrees-C to a V2O5-V3O7 mixture. ImH is successively decomposed from 200-degrees-C and urea is formed as one component of the decomposition product. Vanadium pentoxide is the final decomposition product of both hexavanadates.