Pyrolysis and/or piranha treatment of fluorinated /ozonated single-walled carbon nanotubes (SWNTs) were found to have cut the nanotubes to short length (∼100nm). Pyrolysis of partially fluorinated SWNTs (∼C 5F) at 700°C cut the nanotubes without causing significant crosslinking among the SWNTs. When pyrolyzed at lower temperatures, the fluorinated SWNTs need room temperature piranha treatment to finish the cutting. SWNTs that was ozonated in perfluoropolyethers (PFPE) at room temperature has also been cut when pyrolyzed at 375°C. Functionalization of cut-SWNT with alkylhalide in Li/NH 3(1) was used to debundle the nanotubes into individuals in chloroform for the length measurement. The cut-SWNTs have been characterized by Raman and AFM. AFM shows cut-SWNTs with a length distribution mainly between 30nm and 100nm. Large scale cutting of SWNTs would lead to novel applications of nanotubes in microelectronics, biological imaging and sensing, drug delivery and composite material, etc.