A variety of structural and morphological forms of carbon nanofibers, which comprise perpendicularly and obliquely stacking graphite fibers and the two composite forms made of outer coaxial graphite tubes and inner perpendicularly or obliquely stacking fibers, were fabricated in catalytically decomposing propylene-hydrogen mixture over carbon nanotube-supported nickel catalysts. The growth mechanism for composite carbon nanofibers was proposed. The different types of carbon filaments are promising to be applied in catalyst support and capsules for drug delivery or nanoscale electrical devices.