Exchange bias effect was first discovered in 1956 - 1957 by Meiklejohnand Bean in fine ferromagnetic (FM) Co particles with a shell of antiferro-magnetic (AFM) CoO. This effect is the shift of hysteresis loop along thefield axis and usually appears when FM/AFM hybrid system is cooled below the AFM Neel temperature in the presence of an external magnetic field. Since its discovery, extensive research has been devoted to exploring and understanding the exchange bias in many different systems such as bilayers, core-shell nanoparticles and inhomogeneous materials. The exchange bias effect has been extensively reported in Co/CoO and rarely reported in Co/Co3O4 bilayer thin film .This effect has been also observed in Co3O4 nanostructures in which the FM part comes from the particles/nanowires surface. In this study, we report the exchange bias in a nanostructure containing the both AFM cobalt oxides, CoO and Co3O4 . Co/Cobalt Oxide nanoparticles were synthesized using a mixture of cobalt acetate and polyvinyl acetate as precursors followed by heating between 300–600 °C. The structural characterization was performed by X-ray powder diffraction (XRD) and TG-DSC. The morphology and particle size distribution were determined from transmission electron microscopy (TEM(. magnetic measurements were carried out using a superconducting quantum interference device (SQUID, Quantum Design) magnetometer. The lower temperature sample (300 ? C) is composed of Co, CoO and Co3O4, while the higher temperature synthesis sample only contains Co3O4. All the samples exhibit exchange bias effect. The exchange bias is observed below 204 K (below the CoO blocking temperature) for the sample prepared at lower temperature (300 ? C), while for other samples (350-600 ? C), the effect is observed below 35 K (below the Neel temperature of Co3O4, TN =40 K). The roles of CoO and Co3O4 on the magnetic properties and the mechanisms governing exchange bias effect have been discussed.