The imidazolium-based supported ionic liquids (IL) in activated carbon (AC) is an exciting strategy for developing new adsorbents for H2S removal from biogas. In this work, the influence of IL on AC was discovered by examining the effect of ultrasonic stirring as an impregnation method, AC particle size and IL anion type. AC300μm-[Bmim]Cl-U5 demonstrated the highest H2S adsorption capacity of 8.25±0.38 mg H2S/g and was obtained through [Bmim]Cl impregnated on 300 μm AC size through the ultrasonic stirring for five minutes at room temperature. Adsorption/desorption study confirmed the regeneration ability of AC300μm-[Bmim]Cl-U5 up to three cycles with a maximum adsorption capacity of 14.24±0.43 mg H2S/g. The SEM images confirmed the presence of IL on the AC surface and were further explained through BET analysis. TGA measurement indicated the thermal stability of pristine IL, the fresh and exhausted adsorbent. Therefore, this study proves the potential of ultrasonic-assisted supported IL as a promising adsorbent for H2S removal from biogas that exhibit excellent properties in high adsorption capacity and thermal stability.