A water-soluble carbon nanotube (CNT) wrapped with self-assembly material, and a method for preparation thereof, in which a mixture of the self-assembly material and CNT is provided, and the mixture induces a self-assembly of the self-assembly material on the CNT, thereby wrapping the CNT with the self-assembly material. Water-soluble CNT wrapped with self-assembly material is readily prepared by this method. The CNT wrapped with self-assembly material has excellent applicability in comparison with usual CNT because of its water solubility. Biosensors can be fabricated by selectively attaching to the CNT wrapped with self-assembly material, receptors that bind to or react with target biomaterials or organic compounds.