In this study, a sulfur-coated magnetic carbon nanotube composite was synthesized through coating an elemental sulfur layer onto magnetic carbon nanotubes using a facile thermal process and subsequently employed for fabricating an Ag sensor. The influence of effective parameters including buffer pH, modifier dosage, and preconcentration time were also optimized using the differential pulse voltammetry method. A calibration curve was obtained in the range of 0.5 to 85 µg L⁻¹ under optimal experimental conditions. The detection limit was calculated to be 0.1 µg L⁻¹ based on the 3σ criterion. Real sample analysis including dam, well, and lake waters was successfully performed using the standard addition protocol. The sensor demonstrated satisfactory reproducibility with an RSD value of 3.5%. The sulfur coating, by creating specific binding sites for silver ions, dramatically enhances selectivity and sensitivity of the suggested method. The proposed method for Ag determination exhibits high efficiency and possesses applicability for routine analysis of environmental waters. The low detection limit, wide linear range, and remarkable selectivity, introduce this sensing system as an effective analytical tool for monitoring silver pollution in aquatic environments.