A reduction of Fe3O4 nanowires in nanoscopic reactors of amorphous C:H nanotubes (a-CNTs) was taken to understand features of the chemical reaction mechanism in nanoscale reactors. Fe3O4 nanowires encapsulated in a-CNTs were reduced into iron at a relatively low temperature of 570 degrees C, producing iron nanoparticles encapsulated in CNTs accompanied by the crystallization of the a-CNT shell. It was found that carbon in the a-CNT shell rather than hydrogen (5.5 wt % in it) reduced Fe3O4, showing features different from those in a macroscopic system. The possible mechanisms behind this phenomenon are discussed.