Bismuth molybdenum titanium oxides were prepared in a highly dispersed state by the sol-gel method and in a largely crystallized state by coprecipitation and impregnation. The catalysts contained 14 or 25 wt.% of bismuth molybdate. Their catalytic performance in propene oxidation to acrolein was studied. The increase in activity of Bi-Mo-Ti oxides in propene oxidation as compared to that of bulk bismuth molybdate can be tentatively related, in the case of the sol-gel samples, to the stabilization of small aggregates of Bi- and Mo-containing phases due to the beneficial presence of the titania matrix. The catalytic performance of the samples prepared by coprecipitation or impregnation is enhanced once a crystal size of bismuth molybdate close to 23 nm is reached, i.e., the crystal size should not be too small (samples prepared by the sol-gel method) nor too large (samples prepared by impregnation and coprecipitation), but an optimum size should exist to enhance the catalytic performance. (c) 2005 Elsevier B.V. All rights reserved.