This article outlines the synthesis of gadolinium (Gd)-doped manganese zinc ferrite magnetic nanoparticles (MNPs) as potential magnetic carriers for magnetic fluid hyperthermia (MFH). MNPs with high specific loss power (SLP; 146 Wig) have been developed and used for an in vitro hyperthermia study. The treatment of MFH is fruitful if there is an adequate number of MNPs in tumor cells with the highest SLP to rapidly generate heat while minimizing thermal injury to surrounding healthy tissue. X-ray diffraction patterns of the studied particles confirm the formation of a cubic spinet structure. Field emission scanning electron micrographs showed homogeneous distributions of particles with some agglomerates with a granular appearance. Transmission electron microscopy analysis showed the presence of agglomerated spherical particles at the surface. The substitution of Gd resulted in superparamagnetism at room temperature as confirmed by vibrating sample magnetometer analysis. The estimated saturation magnetization reduced from 48.6 to 28.2 emu/g with an increase in Gd concentration. However, the coercivity increased from 1093 Oe to 1597 Oe. Field cooled and zero field cooled measurements showed Curie temperatures from 315 to 326 K, as required for MFH applications. Cell viability measurements indicated that the MNPs are nontoxic to A549 cells for the studied concentrations of particle fraction and a contact time of up to 24 h. The interaction of the MNPs with A549 cells was highlighted from an image captured by an inverted microscope. In order to treat cancer in vivo, an in vitro hyperthermia study has initially been carried out with A549 cells. (C) 2019 Elsevier Inc. All rights reserved.