The cobalt/polyacrylonitrile (Co/PAN)-based carbon fibrous composites were prepared. The PAN incorporated with cobalt ions was in situ polymerized by initiating the complex solution of acrylonitrile (AN)/cobalt (II) chloride (CoCl2) in which the contents of cobalt ions were 0 wt.%, 0.29 wt.%, 0.56 wt.% and 1.14 wt.%, respectively. The ultrathin blue fibers were formed from the cobalt/PAN composites by the electrospinning method. The electrospun cobalt-incorporated PAN fibers were successfully stabilized in air and subsequently carbonized to form the carbon fibrous composites in a nitrogen (N2) atmosphere. Based on the scanning electron microscopy (SEM), we noticed that beads and beaded fibers were produced during the electrospinning process. When the content of cobalt ions in the complex solution was as high as 1.14 wt.%, there were many honeycomb-like structures and nanopores formed in both stabilized and carbonized fibers. The X-ray photoelectron spectra (XPS) were used to characterize the structure of the composite fibers.