Nanosized powders y(SrTiO3)/(1- y) Sm0.03CoFe1.97 O4 composite, where 0 ≤ y ≤1 is the weight % of SrTiO3, were synthesized by citrate precursor method. The composite was characterized by using X-ray diffraction. The data confirmed the existence of the two phases SrTiO3 (STO) and Sm0.03CoFe1.97O4(SCFO) without remarkable change in the values of their lattice parameter ''a''. The energy dispersive X-ray(EDX) results show that the chemical composition is nearly the same as the nominal stoichiometry. The microstructure properties were investigated by scaning electron microscopy(SEM) and high resolution transmission electron microscope (HRTEM), the magnetic properties were investigated using magnetic susceptibility and vibrating sample magnetometer (VSM). The data refers to the ferrimagnetic nature of all nanocomposites under investigation, also the introduction of Sm ions into CoFe2O4 seems to enhance the magnetic moment by the 4f-3d interaction.