The first-principles study was utilized to study the adsorption behavior of the toxic gases (CO, COS, NO, NO2, NH3, and SO2) on the Fe-decorated antimonene (Sb) monolayer. Antimonene is extensively researched for use in many applications because of its amazing features. The adsorption of gases on the Fe-decorated Sb monolayer showed that it is energetically favorable. CO, COS, NO, and NO2 gases showed chemisorption behavior while NH3 and SO2 showed physisorption. The decoration of Fe on Sb changed its semiconducting behavior to metallic. The higher adsorption energy values (-2.35 eV, −2.31 eV, −3.69 eV, −2.19 eV, −0.24 eV, and −1.54 eV) of the gases (CO, COS, NO, NO2, NH3, and SO2) on Fe-decorated Sb concluded that the material is preferable than Pure Sb. Strong hybridization was seen between the d-orbital of Fe-decorated Sb and the gas molecules in the valance band resulting in improved electronic properties. Structural properties, adsorption analysis, transfer of charge, the density of states (DOS), and analysis of frequency shift, transmission, and recovery time were investigated in detail. All the gases showed a small desorption time except NO while studying the recovery time analysis and suggested that the material appeared as a reversible sensor.