Abstract(#br)A sensitive electrochemical sensor for determination of hydroxylamine has been introduced. This sensor profits by promazine hydrochloride (PHC) as homogenous mediator and multiwall carbon nanotubes to improve the surface of carbon paste electrode as working electrode. Cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry, and differential pulse voltammetry (DPV) are used to study of the suitability of promazine hydrochloride, at the surface of multiwall carbon nanotube paste electrode (MWCNTPE), as a homogenous mediator for the electrocatalytic oxidation of hydroxylamine in aqueous solutions. Hydroxylamine hardly oxidizes at about +1.1V at the carbon paste electrode (CPE), whereas catalytically oxidizes in presence of PHC as mediator at... the MWCNTPE. The electrocatalytic peak current of hydroxylamine oxidation shows a linear dependence on hydroxylamine concentration in the range of 0.008–0.100μM, by DPV in optimized conditions at pH 9.0. In addition, using LSV and in same conditions calibration plot was obtained at hydroxylamine concentration in the range of 0.17–10.0mM. The detection limit (3 σ ) was obtained 1.4nM and 4.2μM for DPV and LSV, respectively. Also, sensitivity in the DPV measurement was 476μA/μM. Kinetic parameters such as electron transfer coefficient, α and diffusion coefficient, D , are also determined. The proposed method was successfully applied as a highly sensitive, selective, simple, and precise method for hydroxylamine determination in the real samples.