In this study, a simple modified glassy carbon electrode with Polydopamine-multiwalled carbon nanotubes (GCE/PDA-MWCNTs) is described for selective and sensitive simultaneous voltammetric determination of dopamine (DA), acetaminophen (AC), and xanthine (XN). A detailed investigation by field emission scanning electron microscopy, Fourier transform infrared spectroscopy and electrochemistry methods such as cyclic voltammetry (CV), electrochemical impedance spectroscopy, differential pulse voltammetry (DPV) and chronoamperometry are performed in order to elucidate the preparation process and properties of the GCE/ PDA-MWCNTs. The proposed modified electrode displays intense and indelible electrooxidation response for simultaneous determination of DA, AC, and XN to three well-separated peaks in the potential range from 0.0 to 0.8 V/Ag/AgCl using CV and DPV methods in phosphate buffer solution with pH 7.0. Under the optimum conditions, detection limits of 20, 30 and 50 nM were obtained for DA, AC and XN, respectively. Moreover, GCE/PDA-MWCNTs was successfully used for simultaneous determination of DA, AC and XN in real samples.