In this work, a series of PEGylated manganese-zinc ferrite mixed (PEG-Mn 1-x Zn x Fe 2 O 4 ) nanoparticles with varying concentrations of zinc ions (x = 0.0, 0.25, 0.4, 0.5, 0.75, 1.0) were synthesized using a solvothermal approach to investigate their physicochemical and magnetic hyperthermia properties through a range of analytical techniques, including TEM, XRF, XRD, FTIR, VSM, and magnetic hyperthermia. The PEG-Mn 1-x Zn x Fe 2 O 4 nanoparticles exhibited a nearly spherical shape and diameters less than 30 nm. The particle size decreased from 27 to 11.6 nm with an increasing amount of zinc (x = 0.0–0.5). The saturation magnetization (M S ) value decreased with the rising Zn content, ranging from 77.8 to 30.7 emu/g. The addition of zinc led to a reduction in the specific absorption rate (SAR) of the material. This decrease in the SAR parameter was associated with a decline in the intrinsic loss power (ILP) value, varying from 0.264 nH m 2 /kg for MnFe 2 O 4 to 0.037 nH m 2 /kg for ZnFe 2 O 4 . Consequently, these PEG-Mn 1-x Zn x Fe 2 O 4 nanoparticles exhibit potential as candidates for magnetic fluid hyperthermia applications.