Nanoparticles Ni_0.7Zn_0.3Fe₂O₄ is fabricated by a sol-gel method. The magnetic and structural properties of powders were investigated with XRD, SEM, Mössbauer spectroscopy, and VSM. Ni_0.7Zn_0.3Fe₂O₄ powders annealed at 300℃ have a spinel structure and behaved superparamagnetically. The estimated size of Ni_0.7Zn_0.3Fe₂O₄ nanoparticle is about 11 nm. Ni_0.7Zn_0.3Fe₂O₄ annealed at 400 and 500℃ has a typical spinel structure and is ferrimagnetic in nature. The isomer shifts indicate that the iron ions were ferric at the tetrahedral (A) and the octahedral (B). Blocking temperature (T_B) of Ni_0.7Zn_0.3Fe₂O₄ nanoparticle is(T_B) of Ni_0.7Zn_0.3Fe₂O₄  about 260 K. The magnetic anisotropy constant of (T_B) of Ni_0.7Zn_0.3Fe₂O₄   annealed 300℃ were calculated to be 1.7×10⁶ ergs/cm³. Also, temperature of the sample increased up to 43℃ within 7 minutes under AC magnetic field of 7 MHz.