PFO(pyrolized fuel oil), which is the bottom oil from a NCC(naphtha cracking center), was initially heat-treated at 300℃ for 2hr under N₂ blowing to remove the volatile matters from the original constituents of the feedstock. The nonvolatile precursor-pitch derived from the PFO raw material was thermally pyrolized in the temperature ranges from 350℃ to 450℃ for 3 hr during the second thermal stage under 500cc/min N₂ blowing. Spinnable isotropic pitch with the softening point of 255℃ and the toluene insolubles of 28wt% was obtained at 370℃, and then was successfully spun through a 0.5mm capillary sized-spinneret. After spinning, an isotropic carbon fiber of 25㎛ diameter was obtained via oxidation and carbonization procedures. Mesophase spherules began to be observed from the second-stage product pitch pyrolized at 410℃, and bulk mesophase with a flow texture was observed at 430℃ and 450℃.