In this work, adsorbents granular activated carbon (GAC), granular activated carbon with acetylene (CVD/GAC) and zeolite A were applied for carbon dioxide (CO 2) and hydrogen sulphide (H 2 S) gas removal. The adsorbents were characterised by scanning electron microscope (SEM) and X-ray diffraction (XRD). Polyethyleneimine (PEI) in ethanol with initial concentration of 0.2 g l-1 and 1 mol dm-3 lithium nitrate (LiNO 3) were prepared to improve the adsorption capacity. In the impregnation process, various adsorbents, i.e., GAC, CVD/GAC and zeolite A were placed in a vial containing 0.2 g l-1 of PEI and 1 mol dm-3 of LiNO 3 solution, at different ratios of adsorbent and various solutions of 30%W/W. The adsorbents (GAC, PEI/CVD/GAC:PEI/GAC, LiNO 3 /CVD/GAC:LiNO 3 / GAC, zeolite 5A, PEI/zeolite 5A and LiNO 3 /zeolite 5A) were tested by using the synthetic biogas (45% CO 2 , 10% N 2 , 45% CH 4 and 105 mg dm-3 of H 2 S). The performance of CO 2 and H 2 S adsorption results have shown that PEI/CVD/GAC is the best adsorbent for low concentration of H 2 S and LiNO 3 /5A is the best adsorbent for CO 2 adsorption. The purity of the outlet methane was 96.6%,