The properties of natural crystalline molybdenum disulfide (MoS₂) nanopowder were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, selected area electron diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and elemental mapping. In addition, the Congo red (CR) dye (adsorbate)-MoS₂ (adsorbent) relationship was investigated. Moreover, the influence of significant factors including pH, temperature, concentration, and time on the adsorption performance of MoS₂ nanopowder was investigated. The MoS₂ nanopowder exhibited excellent decolorization property. The adsorption isotherm data were best fitted with the Langmuir model, and the calculated maximum adsorption capacity was 80.64 mg/g at 50 °C. In addition, the pseudo-second-order model well-fitted the adsorption kinetics data. The adsorption was a physical process involving electrostatic attraction and the optimum conditions for CR adsorption were determined by the Taguchi method. The reusability test results proved that MoS₂ is economical and can be efficiently employed for environmental remediation.