The electrochemical oxidation of hydroxylamine catalyzed by 2,2,6,6-tetramethyl-4-acetylpiperidine-1-oxy (TMAPO) radical at a glassy carbon electrode in phosphate buffer solution has been studied. The reaction mechanism was investigated, and the rate constant for the catalytic reaction evaluated by differential pulse voltammetry is (4.4±0.2)×104M−1.s−1. The plot of the catalytic peak current vs. the concentration of hydroxylamine is linear in the range of 2×10−5– 1×10−2M. A voltammetric method for the analysis of hydroxylamine was proposed based on the linear relationship and the method was used successfully for determining hydroxylamine in the presence of nitrate, nitrite and ammonia.