A novel poly-sulfosalicylic acid-modified glassy carbon electrode (PSA/GCE) was developed for the detection of roxithromycin (RM) and its simultaneous determination with dopamine (DA). The morphologies and interface properties of the PSA film were examined by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Fourier transform infrared (FTIR) spectra indicated that PSA was successfully modified on the electrode. The electro-catalytic oxidation of RM on the PSA/GCE was investigated, individually and simultaneously, using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) under optimum conditions. The proposed method exhibited a wide linear dynamic range from 2 × 10⁻⁸ to 1 × 10⁻⁵ M with a low detection limit (S/N = 3) of 6.67 × 10⁻⁹ M for roxithromycin. The modified electrode showed good stability, reproducibility and high selectivity, and demonstrated its feasibility for analytical purposes and human serum samples.