The hydrogen diffusion studies in MmxTb1-xCo2-H (x = 0, 0.1 and 0.2) have been performed in the hydrogen solid solution phase (α-phase) by measuring the time dependence of hydrogen pressure during the hydrogen absorption process. The measurements were carried out between 500 and 700 °C, and pressures 50, 70 and 90 mbar, respectively, and the diffusion coefficient data are described by an Arrhenius relation. Thermodynamic parameters namely partial enthalpy and the chemical potential of dissolved hydrogen have been determined from the pressure composition isotherm. The dependence of diffusion coefficient, activation energy and the chemical potential of the dissolved hydrogen on the alloy content in MmxTb1-xCo2-H (x = 0, 0.1 and 0.2) have been discussed. © 2006.