Bimetallic Au-Pd NPs with a mean particle size of ca. 1.7 nm were prepared by colloidal synthesis with PVA as a stabilizer and immobilized on various ceria and titania nanostructures. The catalysts were characterised by TEM, XRD, XPS, ICP-AES, and their catalytic performance assessed in the solvent-less selective oxidation of benzyl alcohol. It is shown that even with a technique such as sol-immobilization, the final particle size is sensitive to the physiochemical properties and morphology of the support. In particular, ceria nanostructures were found to be more effective at stabilizing colloidal Au-Pd NPs than titania. Among the ceria nanostructured supports investigated, Au-Pd/ceria nanorods exhibited the highest catalytic activity (TOF > 34,700 h−1) and highest benzaldehyde yield. The particle size of the supported Au-Pd was found to be correlated with the surface area and concentration of Ce3+ and oxygen vacancies in the ceria nanostructures. Overall, the catalytic activity of supported bimetallic Au-Pd catalysts is likely to be governed by a complex interplay of contributions from the particle size, and support morphology, structure and properties.