A method for preparing hydroxylamine, comprising the steps of: (i) pretreating the acidic buffer solution with the compounds having a functional group represented by formula (I), thereby removing metal impurities from the acidic buffer solution; and (ii) reducing nitrate ions in the acidic buffer solution with hydrogen to give hydroxylamine in the presence of catalysts, According to the present invention the selectivity for reducing nitrate ions to give hydroxylamine can be significantly enhanced.