The influence of ZSM-5 composition on the mechanical strength of extruded alumina–ZSM-5 catalysts is studied. For samples with zeolite content ranging from 0 to 95 % and Si/Al ratios of 11.5, 15, and 25, the compressive strength was measured and described by a normal distribution and Weibull statistics. Strength depends non-linearly on zeolite content, peaking at 20 wt. % for all series. ZSM-5 with Si/Al = 15 yields statistically higher strength than Si/Al = 11.5 or 25. The Weibull modulus increases with zeolite content, indicating a more homogeneous granule structure. The observed differences are attributed to the particle size distributions: maximal strength occurs when the bimodal ZSM-5 distribution efficiently complements the pseudoboehmite particles, ensuring optimal packing and binding.