The water-gas shift (WGS) and methane steam-reforming (MSR) reactions over 1% Li/MgO catalyst were investigated using thermal-programmed desorption (TPD) technique with isotope labelled compounds ((CO)-O-16, (H2O)-O-18, (CO)-O-16,d CD4). The experimental results show that WGS reaction over 1% Li/MgO catalyst takes place in the temperature range 400-800 K following a Langmuir-Hinshelwood mechanism. The highest reaction rate was observed at 617 K and the estimated activation energy, from the desorption peak of reaction product, is 158 kJ/mol: The experimental results suggest that the contribution of WGS side reaction to the total amount of CO2 and H-2, formed in the oxidative coupling of methane (OCM), is important. The MSR reaction between CD4 and water over Li/MgO catalyst could not be evidenced by TPD method due to the weak adsorption of CD4. However, a room-temperature isotope exchange between CD4 and the hydroxyl groups of 1% Li/MgO could be observed.