Today, the emission of poisonous gases in the atmosphere has caused many serious health and environmental problems. So, the finding of efficient methods for the reducing or removing of these toxic gases from the atmosphere is of great interest. The main goal of this study is to compare catalytic activity of Pd- and Ni-doped boron nitrite nanosheets (Pd-/Ni-BNNS) for the reduction of nitric oxide (NO) by CO molecule. To this aim, density functional theory (DFT) calculations are performed to calculate adsorption energies, geometric parameters, charge-transfer values and reaction barriers. The results of DFT calculations show that the reduction of NO proceeds through a dimer mechanism. At first, two NO molecules are attached together to form (NO)2 dimer. Next, (NO)2 is decomposed into N2O and Oads species. The Oads is then removed by CO molecule: CO + Oads → CO2. All other possible reactions over these surfaces are studied in details. Our findings demonstrate that the catalytic activity of Pd-BNNS for the reduction of NO is higher than that of Ni-BNNS.