In the present contribution we report the explanation of the magnetic behavior of two recently reported 3d-4f compounds [Ni IILTb III (hfac)2]2 and [CuIILTbIII(hfac)2]2 [1] exhibiting strong magnetic anisotropy. Since the Ni II 2Tb III 2 system contains the diamagnetic Ni II ion and the magnetic interaction between two Tb ions is negligible due to the long Tb-Tb distance the magnetic properties of this compound are solely determined by the Tb III –ion. The parameters of the crystal field that splits the ground 7 F6 –multiplet of the Tb III ion have been evaluated with the aid of the exchange charge model of the crystal field (B.Z. Malkin et al., 1987) which takes into account the covalence effects. In this way the energies and wave functions of the Stark levels have been calculated and the principal values of the magnetic susceptibility tensor for the Ni II 2Tb III 2 molecule have been found. The obtained results have been further used for the calculation of the energy pattern and magnetic susceptibility of the Cu II 2Tb III 2 cluster. In this calculation along with the crystal field acting on each Tb III ion we take into account the magnetic superexchange between Tb III and Cu II ions. Two exchange parameters related to two different Tb-Cu distances have been found from the best fit procedure. The calculated principal values of the magnetic susceptibility tensor indicate the presence of strong magnetic anisotropy with the easy axis of magnetization for the CuII 2TbIII 2 cluster. Moreover, the calculated low-lying energy levels form the barrier for the magnetization reversal. This result is compatible with the observed single-molecule magnet behavior of the Cu II 2Tb III 2 molecule.