Carbon nanotubes (CNTs) have been attracting attention because they have characteristic mechanical and electronic properties. It has been reported that single-walled CNTs can induce large deformation without bond breaking. Therefore, it is of interest to elucidate the electronic properties of CNTs under large deformation. We investigate the deformation behavior and the change in the electronic properties of zigzag-type single-walled CNTs with chiral vectors of (8,0), (12,0) and (14,0) under radial compression with semi-empirical band calculations based on the tight-binding method. The resistance against the deformation increases with the deformation, and its behavior depends on the diameter of the CNTs. The CNTs, which have band gap energy at the initial state, become metallic by the compression. (C) 2004 Elsevier B.V. All rights reserved.