We have investigated magnetic, electronic and structural properties of two series of multilayers, (Mn-(d)/ZnO(3 nm))(N) and (Mn-(d)/SnO2(3 nm))(N), deposited onto Si(100) using magnetron sputtering. The nominal Mn layer thickness, d, ranged from 10 to 0.2 nm and the number of layers, N, was increased to keep the total amount of Mn constant. Structural information was deduced from Xray reflectivity and XAS and Mn oxidation state is estimated from its K edge. The ferromagnetic transition temperature, T-C, in those samples where a ferromagnetic order is established, is always above 400 K. The ferromagnetic fraction within each sample evidences an opposite behaviour as Mn layer thickness is reduced and N increased, in ZnO and SnO2 series. While ferromagnetism is favoured in Mn/ZnO increasing d, the maximum value, in Mn/SnO2, is obtained for 0.4 nm Mn layers. A Mn mixed valence state is not a sufficient condition for ferromagnetism. We discuss the origin of this opposite behaviour which is related to the particular phases formed at the interfaces related to the different ability of ZnO and SnO2 to participate and saturate Mn oxide phases.