A simple and highly efficient surface modification method for inorganic nanoparticles is applied to single-walled carbon nanotubes (SWCNTs), and morphological control of the organized films at the air/water interface is achieved. Prolonged ultrasonic treatment with a mixed acid leads to hydrophilization of the SWCNTs. Amphiphilic organo-modified SWCNTs are prepared by reacting an ionic surfactant on the hydrophilized surface. The organo-modified SWCNTs are well dispersed in organic solvents, resulting in a spreading solvent for the monolayer on the water surface. When it precipitates as a solid at the interface, the surface-modified chain is eliminated, and a pure SWCNT film is obtained by transferring the films to the substrate via firing. The distribution of the tube length in the SWCNT monolayer changes depending on the ultrasonic treatment time. In addition, the monolayer on the SWCNT surface becomes dense and is less defected by the "repeated compression-expansion method." Furthermore, when a lysozyme is allowed to act as a subphase, it is adsorbed and immobilized in the SWCNT monolayer nanosheets. Introduction of the SWCNTs at the air/water interface leads to interfacial organization, thus facilitating nanostructural control and strong interaction with biomolecules.