A new size-selected cluster deposition technique referred to as "parallel-deposition" is presented. An ion beam of multi-sized Aun clusters was spatially separated into individual cluster sizes by utilizing a Wien filter and the clusters spatially separated based on their atomic sizes were simultaneously deposited on a SiO2/Si(100) substrate. Parallel-deposited Aun clusters (n = 6, 7, and 8) on the SiO2/Si(100) substrate showed even-odd oxidation behaviour upon exposure to an atomic oxygen atmosphere, demonstrating the potential of this new technique to study the size-dependent properties of deposited clusters in various research fields.