Ruthenium supported on mesoporous sulfated zirconia was tested as a catalyst for the liquid phase hydrogenation of stearonitrile, n-C17H35CN, and compared with Ru, supported on either microporous sulfated zirconia or the zeolite HY. The mesoporous catalyst is significantly more active than the microporous catalyst; the zeolite supported catalyst is inactive under the same conditions. The results illustrate the effect of pore size on the reaction rate for large molecules. Both mesoporous and microporous catalysts show good stability and a high selectivity towards formation of primary amine. The reaction order in hydrogen is positive with both catalysts; the apparent reaction order in nitrile is negative with the mesoporous catalyst but positive with the microporous catalyst. The activation energy of the reaction is about 90 kJ/mol. TPR data show that under the conditions chosen for pretreatment no SO4 reduction takes place; at higher temperature the sulfur is reduced from S6+ to S2-.