Holmium-doped monoclinic KGd(WO4)(2) nanoparticles were synthesized by the mechano-chemical method. The structure and morphology of KGW:Ho 10 at.% nanopowders were investigated with the use of X-ray Powder Diffraction, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Emission and excitation spectra of KGW nanocrystals were also measured using a fluorometer with a xenon lamp and OPO laser source. The influence of nanoparticles of KGW doped with 10 at.% of holmium on the viability of J774.1 mouse BALB/c monocyte macrophage cells was tested by the WST8 assay. Preliminary immunity cell studies demonstrated a high viability of KGW: Ho 10 at%. Hence, these nanoparticles are promising for imaging applications. To characterize and quantify the physical stability of the nanoparticles of KGW: Ho 10 at.% suitable for biomedical applications, nanoparticles of KGW: Ho in the range of 80-200 nm were prepared. (C) 2018 Elsevier B.V. All rights reserved.