Well-crystallized segmented graphite nanofibers were prepared by pyrolysis of acetylene at 600-800 degreesC using foam Ni catalyst. Transmission electron microscopy indicates that this kind of nanofiber looks like a linear array of lens-like segments with nearly equal separation, which consist of well-ordered graphite platelets intermittently stacked perpendicularly to the filament axis. It was found that the catalyst particles adopting thin slice shape and the Flow rate of acetylene are critical for forming segmented graphite nanofiber. The formation mechanism of segmented graphite nanofiber is also discussed.