Carbon nanotubes (CNTs) together with carbon nanofibers (CNFs) have been produced on the surface of and inside mesocarbon microbeads containing Co nanoparticles during their activation with potassium hydroxide (KOH). The resulting CNFs consist of a number of platelet-shaped sub-units with width of about 500 nm and thickness of 50 nm. The CNTs, with diameter of about 200 nm, grow from the inside to the surface of the activated carbon beads. The results indicate that, in addition to the Co nanoparticles, the existence of KOH also plays an important role in the nanocarbon growth.