Carbon filaments and nanometric carbon particles formed from methane on nano-sized Ni-Cu/Al2O3 catalyst at 720-830℃ were investigated with a transmission electron microscope. Bamboo-shaped carbon filaments were found formed at moderate temperatures. Their morphology depends on the amount of copper doped into the catalyst, the composition of the feed gas and the reaction temperature. Under appropriate conditions, a morphologically pure bamboo-shaped carbon filament can be produced. It is likely that the formation of the quasi-liquid state of the metal nanoparticles during the growth of the carbon is critical for the formation of bamboo shape. The sensitivity of the carbon morphologies to the nano-carbon to the characteristics of catalyst and reaction conditions provides some room for the nanosize construction with carbon under moderate catalytic conditions.