Highly crystalline ZnFe1.98Sm0.01Gd0.01O4 nanoferrites were prepared by co-precipitation method for the first time. The nanoparticles were characterized using thermogravimetric and differential scanning calorimetry analysis (TGA and DSC), which shows the thermal behavior of the reagents mixture. XRD analysis confirms the formation of nanocrystalline ferrite phase with Fd3m space group, and the particle size was observed to be 11 nm . The FTIR reveals two based bands of absorption characterize the formation of the spinel structure. An exhaustive study of the magnetic properties, morphology, crystallinity and effects of co-doping Gd3 + and Sm3 + was presented in detail. The average crystallites size was observed to decrease for Gd3+ and Sm3+ co-doping. Magnetic measurements reveal weak ferrimagnetic behavior at low temperature and superparamagnetic at high temperature with a blocking temperature at 55 K.