Disclosed are a nano-sized palladium-doped anion exchange resin catalyst or palladium-doped cation exchange resin catalyst, a preparation method thereof and a method of removing dissolved oxygen in water using the same. The palladium-doped anion exchange resin catalyst exhibits high dissolved oxygen removal efficiency of 99.about.99.99%, and the palladium-doped cation exchange resin catalyst exhibits high dissolved oxygen removal efficiency of at least 97%, and further, dissolved oxygen in water can be removed through a catalytic reaction without the use of additional chemicals, thereby discharging no secondary pollutants. This catalyst is environmentally friendly, can be continuously developed, and can prevent the loss of the palladium catalyst, which is expensive, and thus can be efficiently applied to various fields, including semiconductors, power plants, microbial culture, food and pharmaceutical production, and the fermentation industry.