Part I (B. Mingot et al., J. Catal. 118, 424, 1989) described the preparation and characterization of new unsupported [100]-oriented MoO3 catalysts. In this second part, the catalytic properties of a series of these catalysts have been compared with more conventional vapor-grown MoO3 samples in the propylene oxidation reaction. This study confirms the structure sensitivity of this reaction: the exposed (120) faces, more developed on the [100]-oriented MoO3 crystallites, lead nearly exclusively to acrolein, whereas the basal (010) planes are active in total oxidation. The selectivity for acrolein formation on the (120) faces has been related to the atomic structure of such faces characterized by the presence of dual sites. © 1992.