Type-H and nano Al2O3, particle size 1787 and 163 nm, resp., each topo-modifled with acrylic and/or methacrylic acid, were used as fillers, 0-30 and 0-10 phr, resp., in ethylene/propylene vulcanizates (30 min/160 degrees C). Modification of Al2O3 with methacrylic acid and acrylic acid changed particle size in the type H to 1384 and 1410 nm, and in the nano type to 174 and 161 nm, resp. The original Al2O3 formed sets in the polymer matrix. The Al2O3-filled vulcanizates had higher crosslink dens. and better mech. properties. The modified Al2O3 acted as co-agents in the dicumyl peroxide crosslinking of the rubber. The resulting vulcanizates relaxed the crit. stresses more easily. The nano oxide raised the crosslinking d. considerably.