The nanosized Ni1-xCoxFe2O4 (x=0, 0.1, 0.3, 0.5) ferrite particles were prepared by sol-gel technique. The characterization studies such as XRD, VSM and Vector Network Analyzer have been carried out to explore the crystal structure, magnetic properties and electromagnetic parameters of the samples. The relation of the saturation magnetization, coercivity, complex permeability and permittivity to the cobalt content and the frequency of microwave were analysed qualitatively. The results indicate that all the samples annealed for 2 hours at 800°C exhibit spinel ferrite structure. It is shown that the magnetic loss and dielectric loss are obvious improved for the x=0.1 sample in 0.1-1.5GHz frequency band, but the loss properties decrease when the content of Co continue increasing.