Background: Nowadays, magnetic nanoparticles (MNPs) have received much attention because of their enormous potentials in many fields such as magnetic fluid hyperthermia (MFH). The goal of hyperthermia is to increase the temperature of malignant cells to destroy them without any lethal effect on normal tissues. To investigate the effectiveness of cancer therapy by magnetic fluid hyperthermia, Fe0.5Zn0.5Fe2O4 nanoparticles (FNPs) were used to undergo external magnetic field (f=515 kHz, H=100 G) in mice bearing implanted tumor.Methods: FNPs were synthesized via precipitation and characterized using transmission electron microscopy (TEM), vibrating sample magnetometer, and Fourier transform infrared. For in vivo study, the mice bearing implanted tumor were divided into four groups (two mice per group), namely, control group, AMF group, MNPs group, and MNPs&AMF group. After 24 hours, the mice were sacrificed and each tumor specimen was prepared for histological analyses. The necrotic surface area was estimated by using graticule (Olympus, Japan) on tumor slides.Results: The mean diameter of FNPs was estimated around 9 nm by TEM image and M versus H curve indicates that this particle is among superparamagnetic materials. According to histological analyses, no significant difference in necrosis extent was observed among the four groups.Conclusion: FNPs are biocompatible and have a good size for biomedical applications. However, for MFH approach, larger diameters especially in the range of ferromagnetic particles due to hysteresis loss can induce efficient heat in the target region.