Hydroconversion of n-octane and n-hexane was investigated on a series of platinum loaded mordenite samples with varied framework aluminium (FA1) content. In agreement with previous authors, it was observed that the rate of hydroconversion is first increased almost linearly with the number of FA1 per unit cell, reached a maximum then decreased abruptly as the number of the FA1/unit cell is increased. Using dealuminaled and directly synthesised mordenite samples with very close FA1 contents we reached the conclusion that the variation of the catalytic activity should neither be related to variation of the acid strength nor to changes in diffusion limitation but rather to the ability of the mordenite samples to favour adsorption of the paraffin.