Co-doped spinel-ferrites Ni1-xCoxFe2O4 nanoparticles with an average diameter of 16-40 nm were successfully prepared by co-precipitation method. The lattice parameter of Co-doped spinal-ferrites Ni (1-x) Co(x) Fe2O4 nanoparticles as well as the porosity was found to decrease while the density and grain size increased with increasing the Co concentration (x). The cation distribution has been estimated by X-ray diffraction. The process of functional group has been identified by Fourier transform infrared (FTIR) spectra and the force constants are calculated from these spectra. Thermal behavior of the prepared NiFe2O4 sample is investigated. From the TEM image most of the particles appear spherical in shape; however, some elongated particles are also present in the images. All the samples in question presented very narrow Ms as a function of Hc loops, which is the characteristic of soft magnetic materials. In addition, increasing the Co(x) concentration in the system was found to increase the saturation magnetization and the coercivity. The dielectric and microwave absorbing properties of the products were investigated in Ku-band.