The ability to prepare and functionalize passivated nanosized metal powders was demonstrated using TiO2 films that were deposited via atomic layer deposition (ALD). Metal nanopowders were synthesized from the dehydration and subsequent decomposition of bulk quantities of metal oxalates in a fluidized-bed reactor. The gas-phase TiO2 ALD coating process was used to passivate these particles in situ, which alleviated the need to expose the oxygen-sensitive materials to air. Metal oxalate size reduction was achieved using a cryogenic milling process that reduced the micrometer-sized oxalate feed powder and yielded metal nanopowders with an average primary diameter of similar to 50 nm. The metal oxalates that have received the most attention are those of iron, nickel, cobalt, and copper. Al2O3-based ALD films have been deposited on each of these metals, whereas TiO2:metal nanocomposite powder research has been performed here and is the basis for this work.