Researchers have described the electrochemical method for voltammetric oxidation and determination of oxymorphone at a glassy carbon electrode (GCE) modified with dandelion-like Co3O4 nanoflowers (DL-Co3O4-NF) for the first time. According to the results, there was a noticeable enhancement in the voltammetric response of oxymorphone at the surface of modified electrode. Moreover, oxymorphone was oxidized on the surface of modified electrode at a potential of approximately 0.245 V less positive, compared to that of an unmodified GCE. We described the anodic peak and diffusion-controlled the procedure. With a detection limits of 2.6 x 10(-9) and 3.4 x 10(-9) M for oxymorphone and papaverine, the function of the concentration of oxymorphone and papaverine in the range of 1.0 x 10(-8)-5.75 x 10(-4) M was recognized a proper linear property by the current estimated by differential pulse voltammetry (DPV). In addition, oxymorphone and papaverine can be concomitantly determined applying the mentioned modified electrode. Ultimately, oxymorphone and papaverine were determined in actual samples through successful implementation of the proposed technique. (C) 2019 The Electrochemical Society.