Process for separating xylenes starting from a feed comprising cuts of isomers of aromatic hydrocarbons containing 8 carbon atoms, in a simulated moving bed, by selective adsorption of a xylene isomer in the presence of a desorbent, by means of particles of agglomerated zeolitic adsorbent based on zeolite crystals with a number-average diameter less than or equal to 1.2 μm, wherein the number-average diameter of said particles of adsorbent is between 150 μm and 500 μm and the mechanical strength measured by the Shell method series SMS1471-74 adapted for agglomerates with a size below 500 μm is greater than or equal to 2 MPa.