The isomerization hydrocracking of heptadecane on Pt/H-ZSM-22 was studied in a continuous flow type, fixed-bed, vapor-phase reactor. High yields of skeletal isomerization of heptadecane (90%) were obtained, The low tendency to cracking of isoheptadecane skeletal isomers on the ZSM-22 zeolite is explained by the limited penetration of these molecules into the micropores openings of the zeolite, preventing their cracking via the common beta-scission reaction mechanisms, The reaction mechanisms of hydrocracking in pore mouths can be derived from the experimentally obtained cracking patterns.