The effect of multivalent cations. Ca2+, Ba2+, Y3+ , Ce3+ and La3+ on the agglomeration of Ru clusters on NaY zeolite under oxygen and at high temperature has been investigated with Xe-129 NMR spectroscopy and X-ray absorption fine structure. Multivalent metal cations exchanged into the zeolite suppress neither the migration nor agglomeration of small Ru clusters inside the supercage of NaY zeolite into large metal panicles onto the external surface of NaY zeolite under 1 atm oxygen above 520 K. However, the resultant Ru particle size depends on the type of metal cations exchanged into NaY zeolite.