In order to understand the catalytic activity of the actinide complexes L 2 AnCH 3 (An = Ac, Th, Pa, U, Np and Pu; L = Cl, Cp and Cp*) towards the activation of the C-H bond of methane, relativistic ZORA/DFT investigations have been carried out. The results obtained from Linear Transit (LT) and Intrinsic Reaction Coordinate (IRC) calculations show that the mechanism involved in these reactions starts with a proton transfer from methane to the methyl group of the complex leading to the formation of a four center transition state characteristic of a bond metathesis process. The U(III) and Np(III) complexes exhibit a high ability to activate the methane C-H bond, the activation energies being respectively equal to 10.5, 17.1 and 21.0 kcal/mol for Cl 2 NpCH 3 , Cp 2 NpCH 3 and Cp* 2 UCH 3 respectively whereas the Th(III) complexes exhibit the highest activation energy, 34.9 kcal/mol for Cp* 2 ThCH 3. Since the initial step of the reaction is viewed as a proton transfer, the analysis of the charges evolution and frontier molecular orbitals of the complexes and the transition states, shows that a facile polarization of the bonds involved in the reaction has the effect of reducing the activation energy. The role of the metallic 5f orbitals in the reactivity of the L 2 AnCH 3 compounds towards CH 4 is analyzed and discussed. More important the 5f actinide orbital contribution, less important is the activation energy.