In this work, Co-Ti-N nanocomposite films were prepared by the reactive sputtering method. Depending on N 2 partial pressure in the Ar and N 2 mixture during sputter deposition, two different structures were formed. At an N 2 partial pressure of 6.7x10 - 4 Pa, the as-deposited film is composed of TiN and an amorphous CoTiN phase. After thermal annealing at 400 o C, Co was separated out to form a Co-TiN structure. The saturation magnetization increases substantially after thermal annealing. On the other hand, when the film was deposited at an N 2 partial pressure of 6.7x10 - 3 Pa, both Ti and Co were nitrided. A complex nitride of Ti and Co, (TiCo)N was formed in the film. In this circumstance, thermal annealing at 400 o C had almost no effect on the structure and magnetic properties of the film.