Co/CoO hybrid films are prepared by annealing Co films with various ratio of oxygen of O2/Ar mixture. The nanocomposite film shows a relatively large exchange bias (5.32 kOe) and coercivity (HC-: 6.17 kOe) taken at 80 K when formed by post annealing at 473 K under 3% O2 for 1h. Both are much larger than that of Co/CoO nanocomposite by reactive sputtering with an oxygen partial pressure. Investigation shows that the formation of interface by post annealing is of importance for the large exchange bias and enhanced coercivity. The surface CoO, grain size of CoO and composition may also contribute to magnetic properties of the post annealing film.