In this paper, Co/Al2O3 composite nanofibers with different Co content are fabricated by electrospinning combinedwith selective reduction. By controlling the Co content in the composite nanofiber, not only the fiber’s morphology, but alsothe magnetic properties can be well adjusted to meet different applications’ requirements. The magnetic hysteresis loops ofcomposite nanofiber show two different types of shape, typical ferromagnetism and wasp-waisted ferromagnetism. Interestingly, the saturation magnetization, which has a close relationship with the content of magnetic component, is notsimply shows an increasing tendency with the increases of Co content in the composite fiber. For the Co content below50 wt%, the Ms value increases with the Co content. After that, the saturation magnetization decreases to a valley value atnear 60 wt% Co content, then increases again. The coercivity also shows the same tendency. The results indicate that thedipolar coupling interaction plays a key role in the magnetic property adjustment of Co/Al2O3 composite nanofiber.