Cerium doped cobalt ferrite nanoparticles with chemical formula CoFe1·9Ce0·1O4 were synthesized at different annealing temperatures (600, 700, 800, 900 and 1000C°) via sol-gel auto-combustion method. Thermal analysis for sample annealed at 1000C° was examined through differential scanning calorimetry (DSC) and revealed the presence of exothermic peak at around 500C° attributed to crystallization of prepared nanoferrites. Structural analysis such as phase formation, crystallinity and morphology was investigated by x-ray powder diffraction (XRD) and high resolution transmission electron microscope (HRTEM). XRD study revealed higher dependence of grain size growth with annealing temperatures as compared to lattice parameter. HRTEM investigation confirmed that grains have almost uniform morphology with some agglomeration and confirmed values of lattice parameters and grain sizes calculated from XRD data. Magnetic hysteresis was studied by vibrating sample magnetometer (VSM) at room temperature with an applied field of 20 kOe. The results showed an increase in saturation magnetization and remanent magnetization with increasing of annealing temperature, whereas a decline in coercivity was observed. Distribution of cations at tetrahedral and octahedral sites was investigated using x-ray and magnetic parameters which confirmed the mixed spinel ferrite nature of samples. Dielectric properties were carried out at room temperature in the range 0.1Hz–3.0 MHz. Both dielectric constant and ac conductivity decreased with rising of annealing temperature. Variation of dielectric loss tangent, impedance, electric modulus and relaxation time with temperature were also investigated. The effect of annealing temperature on the structure and its impact on magnetic and dielectric properties has been examined and discussed.