On the basis of a molecular mechanics model, an analytical solution of the radial breathing mode （RBM） frequency of single-walled carbon nanotubes （SWCNTs） is obtained. The effects of tube chirality and tube diameter on the RBM frequency are investigated and good agreement between the present results and existing data is found. The present analytical formula indicates that the chirality and size dependent elastic properties are responsible for the effects of the chirality and small size on the RBM frequency of an SWCNT.
