In the present study, we proposed a simple method to locate defect sites in individual SWNTs with an AFM technique by using a thermal oxidation strategy. After thermal oxidation of well-dispersed SWNTs on a silicon surface in air at 500 degreesC, almost all of the original SWNTs were fractured into short fragments. The range of the fragment sizes was different and closely related to the length and growth time of the tubes. The rupture of SWNTs was confirmed to be a result of the presence of defects in tubes and to be caused by the attack of oxygen molecules in air. Owing to the damage event that occurred in SWNTs after heating treatment, a thermal oxidation method may be developed as a potentially useful technique for the cutting of SWNTs, and chemical functionality of the SWNTs could also be achieved during this process. In this regard, a thermal treatment method would be employed as another useful cutting and functionalizing approach to tailor the chemical and physical properties of SWNTs.