The infrared spectra and stability of CO and H 2 O sorption over Ag-exchanged ZSM-5 zeolite were investigated by using density function theory (DFT). The changes of NBO charge show that the electron transfers from CO molecule to the Ag + cation to form an σ-bond, and it accompanies by the back donation of d-electrons from Ag + cation to the CO (π*) orbital as one and two CO molecules are adsorbed on Ag–ZSM-5. The free energy changes ΔG, −5.55kcal/mol and 6.52kcal/mol for one and two CO molecules, illustrate that the Ag + (CO) 2 complex is unstable at the room temperature. The vibration frequency of C–O stretching of one CO molecule bonded to Ag + ion at 2211cm −1 is in good agreement with the experimental results. The calculated C–O symmetric and antisymmetric stretching frequencies in the Ag + (CO) 2 complex shift to 2231cm −1 and 2205cm −1 when the second CO molecule is adsorbed. The calculated C–O stretching frequency in CO–Ag–ZSM-5–H 2 O complex shifts to 2199cm −1 , the symmetric and antisymmetric O–H stretching frequencies are 3390cm −1 and 3869cm −1 , respectively. The Gibbs free energy change (ΔGH2O) is −6.58kcal/mol as a H 2 O molecule is adsorbed on CO–Ag–ZSM-5 complex at 298K. The results show that CO–Ag–ZSM-5–H 2 O complex is more stable at room temperature.