A presentation of experimental study results obtained by antiferromagnetic resonance (AFMR) of the high-frequency properties of the multiferroic Nd 0.75 Ho 0.25 Fe 3 (BO 3 ) 4 in a broad range of temperatures and frequencies. We studied the effect of substituting the Nd 3þ ions with Ho 3þ , on the resonance properties of the Nd 0.75 Ho 0.25 Fe 3 (BO 3 ) 4 solid solution. In addition, we investigated the particularities of magnetic-field induced spin-reorientation phase transitions for Hjjc and Hjja directions, in which the anisotropy of the magnetic system is measured from "easy-axis" anisotropy to "easy-plane." The AFMR modes of a Fe 3þ subsystem are revealed. New information about the most important characteristics of AFM is obtained, including: frequency-field dependence of the AFMR spectrum, gaps in the spin-wave spectrum, effective magnetic anisotropy values, and fields of spin-reorientation transitions. It is shown that "easy-plane" anisotropy prevails in this magnet, with a weak anisotropy in the basal plane. For the first time there are observed features in the AFMR spectra that could be tied to the presence of a spatially modulated spin structure (incommensurate phase) in AFM Nd 0.75 Ho 0.25 Fe 3 (BO 3 ) 4 . V C 2015 AIP Publishing LLC.