Double-C-60-end-capped poly(ethylene oxide) (FPEOF) exhibited concentration-dependent optical limiting behavior in toluene, THF, and water. Its performance was not only inferior to C-60-toluene solution with similar C-60 concentration, but its linear transmittance was also remarkably lowered by the aggregation Of C-60 in the solutions. Optical limiting studies with poly(ethylene oxide)/FPEOF blends suggested the significance of bimolecular excited-state processes (such as the formation Of C-60 excimers) to the optical limiting performance of FPEOF at 532 nm. Although an aqueous multiwalled nanotube (MWNT) suspension showed only weak optical limiting actions toward laser at 532 nm operating at 20 Hz, its mixing with FPEOF solution resulted in enhanced optical limiting responses. FPEOF/MWNT composites also exhibited optical limiting responses at 1064 nm.