Synthesis of Cu and Ni-Cu particles from their aqueous formate solution by hydrogen reduction in hot-corn pressed water was carried out at 673 K with a titanium alloy autoclave. Hydrogen was produced by thermal decomposition of the formates. Metal particles having an average size of around 500 nm were produced without any additives. Ni-Cu metal alloy particles having different compositions were obtained by changing Cu/Ni niolar ratio in starting solutions.