An electrochemical anodic behavior of hydrochlorothiazide (HCTZ) was studied by using electrochemically pretreated pencil graphite electrode (EPPGE) using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV). Two anodic peaks were observed at peak potential 842mV and 1091mV on EPPGE at phosphate buffer (pH7.0). Electrooxidation process of HCTZ shows diffusion-controlled process on EPPGE. DPV and SWV show a good linearity in the concentration range 4μM to 140μM and 1μM to 20μM, respectively. The limits of detection were found to be 3.25μML−1 and 0.421μML−1, respectively. Electrochemical impedance spectra (EIS) gave the charge transfer resistance at EPPGE (32.3kΩ) and PGE (867kΩ), which shows an increase in the electron transfer rate at EPPGE than that of PGE. Surface area, sensitivity and electron transfer kinetic parameters were studied. Electrochemical pretreatment is a simpler method compared to other modifications for the electrodes and this method could be applied for the sensitive determination of HCTZ present in pharmaceutical formulations and urine samples. Keywords: Cyclic voltammetry, Differential pulse voltammetry, Electrochemically pretreated pencil graphite electrode, Square wave voltammetry