Mesoporous zeolites were successfully synthesized by utilizing carbon black particles during the sol-gel synthesis as a template for the network of mesopores. Mesoporous samples of ZSM-12, and Zeolite Beta were synthesized with this method with an average pore size about 400 A.... The size and the percentage of mesopores increases with the C/Si ratio. Our TEM investigations validate the formation of mesoporous networks and voids. This study proves that this method can be generalized for both high and low aluminum zeolites. Selected samples were tested for the hydroisomerization of n-heptane, a probe reaction of great importance for the upgrading of light naphthas. It was found that under identical operating conditions the mesoporous samples exhibited higher, almost fourfold, activity. The selectivity for C7 isomers was higher over the mesoporous samples in comparison with the regular ones. More specifically, the selectivities towards mono- and dibranched isomers increases monotonically with the degree of mesoporosity. The increase of branching over the mesoporous zeolite samples we observed is due to the combined effect of reduced residence times in the zeolite crystal for the reaction products, and the larger "average" pores of the mesoporous samples that allow the formation of bulkier reaction state intermediates. Moreover, the mesoporous samples resulted in generation of less light hydrocarbons (C3, C4). The above behavior is a testimony of the tremendous potential that mesoporous zeolite crystals offer and could be very beneficial for numerous refining processes.