Mesoporous silver-melamine (Ag-MA) nanocomposites were synthesized simply by the controlled supermolecular self-assembly process to be modified onto the electrodes for the electroanalysis of multiple sulfides in blood or wastewater. It was discovered that Ag-MA nanocomposites could be prepared with various morphological structures depending on the Ag-to-MA ratios. Furthermore, the electrodes modified with mesoporous Ag-MA nanowires could display stable and sharp electrochemical peaks of solid-state AgCl at a considerably low potential approaching zero, thus circumventing any interference from possibly coexisting electroactive substances in the background. More importantly, the yielded AgCl signals would decrease selectively induced by sulfides through the specific sulfide-chloride replacement reactions toward the transferring of AgCl into non-electroactive Ag2S. The developed electroanalysis strategy could facilitate the selective detection of multiple sulfides (i.e., S2- or H2S, Sx2-, cysteine, and S2O32-) in the complicated media with high-level salts such as blood and wastewater, showing a linear concentration range from 0.50 to 512 μM as exemplified for S2- ions in blood. Such an electroanalysis device equipped with the portable electrochemical transducer can be tailored for the field-deployable monitoring of a variety of sulfides in clinical and environmental analysis fields.