The chemical stability Of C-60 molecules encapsulated into single-wall carbon nanotubes (SWNTs), so-called peapods, against oxygen was analyzed by thermogravimetric analysis. The maximum values for the derivative on the weight loss were observed at temperatures higher by 140degreesC than that of the C-60 powder and lower by 40degreesC than that of SWNTs. This means that the outside SWNT prevented the combustion Of C-60 molecules inside the peapods. (C) 2003 Elsevier Science B.V. All rights reserved.