The preparation and electrochemical characterization of a nickel hydroxide modified nickel electrode as well as its behavior as electrocatalyst toward the oxidation of hydrochlorothiazide (HCTZ) were investigated. The electrochemical behavior of the modified electrode and the electrooxidation of HCTZ were explored using cyclic voltammetry. The voltammetric response of the modified electrode in the detection of HCTZ is based on the electrochemical oxidation of the Ni(II)/Ni(III) and a chemical redox process. The analytical parameters for the electrooxidation of HCTZ by the nickel hydroxide modified nickel electrode were obtained in NaOH solution, in which the linear voltammetric response was in the concentration range from 1.39×10(-5) to 1.67×10(-4)molL(-1) with a limit of detection of 7.92×10(-6)molL(-1) and a sensitivity of 0.138μALmmol(-1). Tafel analysis was used to elucidate the kinetics and mechanism of HCTZ oxidation by the modified electrode.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Faculty of Science and Technology, São Paulo State University (UNESP), CEP 19060-900 Presidente Prudente, SP, BrazilFaculty of Science and Technology, São Paulo State University (UNESP), CEP 19060-900 Presidente Prudente, SP, BrazilFAPESP: 2005/01296-4FAPESP: 2013/10469-6