This paper reports a simple approach for the determination of phentolamine mesilate (PM) using a poly(sodium p-styrenesulfonate)-multi-wall carbon nanotube (PSS-MWCNT) modified glassy carbon electrode. PSS-MWCNTs were synthesised via a moderate one-step non-covalent reaction between MWCNTs and PSS. Compared with purified MWCNTs (p-MWCNTs), the introduction of PSS improved the dispersion of MWCNTs and increased the accumulation capability of PM. As a result, the detection sensitivity for PM was greatly enhanced at this voltammetric sensor. The electrochemical properties of PM were first investigated in detail and a reaction mechanism was proposed. Utilizing linear sweep voltammetry, a low detection limit (3.0 x 10(-8)molL(-1)) and a wide linear range (8.0 x 10(-8)molL(-1)-6.0 x 10(-6)molL(-1)) were achieved by the proposed sensor. Finally, the proposed method was successfully applied to the analysis of real-life samples.