In this study, the decomposition of acetic acid to lower fraction products (i.e., CH4, CH3CHO, CO, and CO2) is elucidated using different possible pathways along with their potential energy surfaces under density functional theory (DFT) framework. Furthermore, a kinetic investigation involving evaluations of rate constants, Arrhenius constants and equilibrium rate constants of all elementary reaction steps is carried out at a wide range of temperature (298-698 K) and a fixed pressure of 1 atm. Briefly, results indicate that overall decomposition of acetic acid is favourable through OH cleavage reaction route over both catalyst clusters involving elementary reaction steps of OH cleavage of acetic acid, CO cleavage of acetyl species, and hydrogenation of methyl to produce methane. The decomposition of acetic acid over both catalysts is highly likely to produce methane and CO2 rather producing acetaldehyde which agrees with the existing experimental results. The formation of water from hydrogenation of hydroxyl group is not favourable over both catalyst clusters especially Ru/MgO catalyst. According to the kinetic investigation, the performance of supported Ru catalyst, i.e., Ru/MgO is superior to that of bare Ru catalyst for the decomposition of acetic acid.