Single-walled carbon nanotubes (SWNTs), solubilized individually in dimethylformamide using a polymer with anthracene groups or in aqueous micelle of sodium dodecyl sulfate (SDS), were irradiated with near-infrared (IR) pulsed-laser light. Near-IR light was absorbed by the SWNTs and converted to heat through photothermal conversion of SWNTs, which did not greatly degrade the polymer wrapping the SWNTs. The local and transient heat via the irradiation resulted in SWNT-flocculation with raising the macroscopic temperature of the solution. No such irradiation effect was recognized for the SWNTs/SDS aqueous solution. The present finding reveals that carbon nanotubes act as a 'molecular heater' that triggers structural changes of carbon nanotube nanocomposites. (c) 2006 Elsevier B.V. All rights reserved.