This paper described a facile strategy for ratiometric electrochemical sensing of quercetin (Qu) in electrolyte solution directly using bare glassy carbon electrode (GCE). This strategy mentioned to two kinds of substances with remarkable oxidation current peaks at differential electric potentials, such as thionine (TH) and Qu with oxidation current peaks at -0.22 V and 0.18 V, respectively. Briefly, a GCE was immersed into the electrolyte solution of phosphate buffered saline (0.01 M, pH 6.5, containing 0.15 M of NaCl). Serving as the reference electroactive substance, TH was injected to fabricate a homogeneous electrolyte solution. Afterward, Qu as the analyte was also added to form a facile electrochemical sensing system. Differential pulse voltammetry (DPV) curves of the different sensing systems with increasing concentrations of Qu [Qu] were measured by directly using a bare GCE as the sensing platform. Upon the increase of [Qu], the oxidation current peak intensity of Qu at 0.18 V increased significantly, but that of TH at -022 V hardly any changed. The ratiometric oxidation current peak intensities of Qu to TH (I-QU/I-TH) almost linearly enhanced when the [Qu] increased from 0.1 to 15 mu M, together with a high linear coefficient (R-2 = 0.9932) and a low detection limit (3.1 nM of Qu). The as developed ratiometric electrochemical sensor of Qu exhibited highly selective and sensitive responses to Qu over potential interferences in real food samples, accompanied by high detection recoveries.