<p>The activity and selectivity to light olefins during conversion of naphthenic hydrocarbons over HZSM-12 zeolites depending on the textural and acid properties and the size of the processed molecule were studied. Two ZSM-12 samples were synthesized under hydrothermal conditions, following a single experimental procedure in different reactors. To generate intracrystalline mesoporosity, the synthesized ZSM-12 zeolites were subsequently desilicated under different alkaline treatment (AT) conditions generating the hierarchical zeolites. After to obtain their protonic form, the samples were characterized by XRD, SEM, EDS, N₂ physisorption, ²⁷Al MAS NMR and NH₃-TPD. XRD and N₂ sorption measurements confirmed, respectively, that the MTW (Mobil TWelve) structure of the ZSM-12 zeolite was preserved and that after the AT occurred an increase in the mesoporous volume, consequently increasing the specific external surface area, besides with an increase in the concentration of weak acid sites in the alkaline treated sample under more severe conditions. The catalytic evaluation shows an increase in the conversion of cyclohexane, methylcyclohexane and ethylcyclohexane over the more mesoporous zeolite with the yield to light olefins increasing with the increase of the length of the substitutive alkyl group in the naphthenic molecule.</p>