Porosity and acidity of zeolites are key factors for highly efficient catalyst design. Herein, we investigate the isomerization performance of a high-silica zeolite IM-5 which has a unique limited 2.5 nm "nanoslab" pore structure. Compared with the reference ZSM-5, the higher adsorption amount and rate of IM-5, proven by adsorption experiments of n-heptane and toluene, resulted in a higher isomer selectivity in n-C-7 or n-C-16 hydroisomerization reactions, which increased relatively by 19.5% and 91.5%, respectively. Furthermore, IM-5 also shows higher n-C-7 or n-C-16 conversion due to its more strong acid sites. Additionally, mesopore introduction into IM-5 significantly increases isomer selectivity, especially for long chain n-C-16. The selectivities of C-7 isomers and C-16 isomers of mesoporous M-IM-5 increase relatively by 73.3% and 216.1% compared with microporous IM-5. Mesopores and reduced diffusion length facilitate the mass transport of bulky molecules, then decrease subsequent cracking side reaction that consumes branched isomer products.