Abstract: A process for removing dissolved oxygen from an aqueous medium, using hydrazine to react with the oxygen, where the aqueous medium is contacted with a catalyst bed of palladium or platinum metal dispersed on a solid carrier, at ambient temperatures. The catalyst bed effects reaction of the hydrazine with the dissolved oxygen to provide residual oxygen contents of below 10 ppb. Preferably, the hydrazine is intimately mixed with the aqueous medium prior to contact with the catalyst bed. The process is especially useful in removing dissolved oxygen from recirculating aqueous medium of a steam generation system, where the hydrazine-containing aqueous medium is contact with the catalyst bed after passage through the condenser pump but prior to the feedwater heaters.