Amorphous carbon nanopillars that we fabricated with electron-beam induced chemical vapor deposition were tublized by heating at 600°C-650°C in the presence of iron nanoparticles. The tublization process of the amorphous carbon nanopillar was observed in situ by using transmission electron microscopy and scanning transmission electron microscopy. A molten catalyst nanoparticle penetrated the amorphous carbon nanopillar, dissolving it and leaving a graphite track behind. The nanoparticle moved with its shape changing like the movement of an earthworm. Z-contrast images of the molten catalyst nanoparticle revealed that dissolved carbon atoms were diffused through its outer layer. The tubulization mechanism is a solid-quasiliquid-solid mechanism in which the carbon phase transformation is a kind of liquid phase graphitization of amorphous carbon catalyzed by liquefied metal-carbon alloy nanoparticles. [DOI: 10.1380/ejssnt.2006.401]