The power-to-gas process is an option to transform fluctuating renewable electric energy into methane via water electrolysis and subsequent conversion of H-2 by methanation with CO2. The dynamic behavior of the methanation reactor may then be a critical aspect. The kinetics of CO2 methanation on a Ni-catalyst were determined under isothermal and stationary conditions. Transient isothermal kinetic experiments showed a fast response of the rate on step changes of the concentrations of H-2, CO2; in case of H2O, the response was delayed. Non-isothermal experiments were conducted in a wall-cooled fixed-bed reactor. Temperature profiles were measured and the effect of a changing volumetric flow was studied. The experimental data were compared with simulations by a transient reactor model.