Desorption of molecular hydrogen from single-walled carbon nanotube (SWNT) bundles and peapods (C 60 encapsulated SWNTs) have been observed at about 350 K by the temperature-programmed-desorption (TPD) method. A treatment with NaOH after purification is found to be crucial for obtaining clean SWNTs and for desorbing hydrogen at this moderate temperature. A clear difference observed in gas evolution from SWNTs and peapods shows that the storage site for the hydrogen molecule is an inter-tube space and that 'sub-nanometer' sized spaces are indispensable for storing hydrogen molecules in this system. © 2002 Elsevier Science B.V. All rights reserved.