¹Department of Analytical Chemistry, Faculty of Pharmacy, Gazi University, Ankara, Turkey DOI : 10.29228/jrp.240 In this study, a paper-based electrochemiluminescence (ECL) sensor was developed for the determination of diltiazem hydrochloride (DTZ-HCl), which is a vasodilator of the calcium channel blocker. Herein, the ability of DTZ to act as a co-reactant for Ru(bpy)32+ in the ECL system was utilized. The pharmaceutical dosage forms were studied to verify the applicability of the developed ECL method. A paper electrode was fabricated by mimicking commercial screen-printed electrodes (SPE) and decorated with gold nanoparticles by using an electrodeposition technique in order to enhance the ECL signals. To generate the excited states of the Ru-(bpy)32+/DTZ-HCl pair, the potential in a range from -0.5 to 1.3 V at a scan rate of 100 mV/s was applied by utilizing cyclic voltammetry (CV) to the gold nanoparticle decorated paper electrode (AuNPs@PE). The ECL signals were recorded using the μStat ECL potentiostat, which is controlled by DropView 8400 Software, concurrently. The coefficient of determination and limit of detection obtained from the standard addition method were found as 0.997 and 0.12 μg/mL, respectively. Furthermore, the usage of conventional SPE electrodes confirmed that the results obtained by the developed method were acceptable with the similarity of 97.2% in terms of average recovery value, for the detection of DTZ-HCl in pharmaceutical dosage forms. This study is a startup method to develop highly selective paper-based ECL sensors in routine drug analysis that is fast and low cost. Keywords : electrochemiluminescence; ECL; paper electrode; diltiazem; pharmaceutical