Abstarct: In the present research, the effect of vacancy defects on natural frequencies of carbon nanotubes is investigated and thermoelastic damping in these materials is discussed. The geometric structure of single-walled and double-walled nanotubes is obtained through programming and therefore, the defects in each nanotube model are simply generated by removing one or more atoms from the structure. Molecular dynamics simulations of nanotube vibrations are conducted using special software. In the problems considered, many parameters are varied in order to do a comprehensive analysis of the systems’ responses. Natural frequencies of a nanotube are determined by means of a transform from the time domain to the frequency domain. The results show that in most cases, the existence of a single vacancy or vacancies with a random distribution causes a reduction in the fundamental natural frequency of the system. However in some of the problems, the variation of frequency shift percent with the position of a single vacancy along a nanotube’s axis or with the concentration of vacancy defect does not follow a specific trend. It is also noteworthy that the values calculated for the quality factor of nanotubes at room temperature are small and as in the particular conditions provided the inverse of quality factor represents thermoelastic damping, this form of damping leads to significant energy dissipation in the nanotubes at room temperature. Finally, the dependence of thermoelastic damping on temperature and the effect of a single vacancy on dissipation in nanotubes are discussed in this thesis.