Abstract We study experimentally and theoretically the dynamics of spin relaxation motion excited by a femtosecond pulse in the TbCo 2 /FeCo multilayer structures with different ratios of TbCo 2 to FeCo thicknesses r d = d T b C o 2 / d F e C o . The main attribute of the structure is in-plane magnetic anisotropy that is artificially induced during sputtering under a DC magnetic field. The optical pump-probe method revealed strongly damped high-frequency oscillations of the dynamical Kerr rotation angle, followed by its slow relaxation to the initial state. Modeling experimental results using the Landau–Lifshitz-Gilbert (LLG) equation showed that the observed entire dynamics is due to destruction and restoration of magnetic anisotropy rather than to demagnetization. For the pumping fluence of 7 mJ cm −2 , the maximal photo-induced disruption of the anisotropy field is about 14% for the sample with r d = 1 and decreases when r d increases. The anisotropy relaxation is a three-stage process: the ultrafast one occurs within several picoseconds, and the slow one occurs on a nanosecond time scale. The Gilbert damping in the multilayers is found to be one order of magnitude higher than that in the constituent monolayers.