The nano-sized Mn0.5Zn0.5Fe2O4 spinel-type ferrite was synthesized by sol-gel auto-combustion method using citric acid as the chelating agents. The analysis methods of FT-IR, XRD, wave-guide were used to character the gel and the products after calcining. From the results, it was shown that the homogeneous organic complex base salts were formed in the process of gelation formation. The crystalline sizes of as-synthesis powders, calcined at 700°C for 2h and calcined at 1000°C for 2h were 15nm, 21nm and 25nm, respectively. The nanocrystalline had both dielectric loss and magnetic loss in the frequency range of measurement. The electron transportation of Fe2+↔Fe3+ can make the resistivity reduce to result in a certain amount of dielectric loss.