We present a novel functionalization scheme for single-walled carbon nanotubes (SWNTs) to afford nanotube-biomolecule conjugates with the incorporation of cleavable bonds to enable controlled molecular releasing from nanotube surfaces, thus creating "smart" nanomaterials with high potential for chemical and biological applications. With this versatile functionalization, we demonstrate transporting, enzymatic cleaving and releasing of DNA from SWNT transporters, and subsequent nuclear translocation of DNA oligonucleotides in mammalian cells. We further show highly efficient delivery of siRNA by SWNTs and achieving more potent RNAi functionality than a widely used conventional transfection agent. Thus, the novel functionalization of SWNTs with cleavable bonds is highly promising for a wide range of applications including gene and protein therapy.