Multilayer carbon nanotubes formed by the mechanical activation obtained by the mechanical activation of amorphous carbon are investigated. The amorphous carbon is produced by the pyrolysis of plant matter—specifically, brown sphagnum moss (Sphagnum fuscum) and Magellan’s peat moss (Sphagnum magellanicum), corn shoots, spiny bamboo (Bambusa blumeana schultes), cotton, and okra stalks (Abelmoschus esculentus). The carbon nanotubes are formed by pyrolytic and mechanochemical technology. Amorphous carbon is produced at 950°C and then subjected to mechanochemical treatment in a planetary mill for 1–46 h. The amorphous carbon is removed by three-stage vacuum annealing at 220–870°C. The greatest quantity of carbon nanotubes is produced after 36-h mechanical activation, for all types of nanopowder. More prolonged mechanical activation leads to the formation of (20–100)-μm aggregates, and the thermal stability of the multilayer nanotubes is lost.