In order to investigate magnetic structure and the mechanism of the Curie temperature (TC) enhancement in TbNi4Co and TbNi 4Fe compounds in comparison with TbNi5, electronic structure calculations were performed within the LSDA U method (local spin density approximation with Hubbard U-correction). Magnetic moments for Ni, Fe, and Tb ions resulted from the LSDA U calculations for TbNi5 and TbNi4Fe compounds were found to be in very good agreement with the ones refined from the neutron data. Experimental magnetization measurements demonstrate a substantial increase of TC in TbNi4Co (TC ∼ 60 K) and especially in TbNi4Fe (TC ∼ 280 K) in comparison with TbNi5 (TC ∼ 23 K) that correlates with the growth of the exchange-interaction parameter in the 3d sublattice calculated in the present work. © 2011 American Institute of Physics.