The influence of interdiffusion on the magnetic properties of Co/Cu/Co trilayers after annealing in the presence of a strong magnetic field was investigated. The interdiffusion zone of films that were annealed at temperatures of 573 K and 773 K in the presence of high magnetic fields were not affected. However, the interdiffusion zone of films annealed at 673 K in the presence of a high magnetic field increased significantly due to phase transformation. Meanwhile, the high magnetic field has an influence on alloying process by affects the concentration distribution of Co and Cu across the interface because of magnetic force. The change in the interdiffusion, caused by high magnetic field annealing, decreased the content of the magnetic phase. This decreasing in the magnetic phase reduced the saturation magnetization. The coercivity decreases in the sample annealed at 673 K with a high magnetic field can result from not completely alloying compared with non-field case. (C) 2016 Elsevier B.V. All rights reserved.