ABSTRACT:We reviewed and examined recent progresses related to the nanochemistry and nanobiology of signalwalled carbon nanotubes (SWCNTs), focusing on the diameters of SWCNTs and how the diameters affect the interactions of SWCNT with protein and DNA, which underlay more complex biological responses. The diameters of SWCNTs are closely related to the electronic structure and surface chemistry of SWCNTs, and subsequently affect the interaction of SWCNTs with membrane, protein, and DNA. The surfaces of SWCNT with smaller diameters are more polar, and these with large diameters are more hydrophobic. The preference of SWCNT to interact with Trp/Phe/Met residues indicates it is possible that SWCNT may interfere with normal protein-protein interactions. SWCNT-DNA interactions often change DNA conformation. Besides the promising future of using SWCNTs as delivering nanomaterial, thermal therapy, and other biological applications, we should thoroughly examine the possible effects of carbon nanotube on interrupting normal protein-protein interaction network and other genetic effects at the cellular level.