DNA-wrapped single-wall carbon nanotubes (DNA-SWNT hybrids) under various humidity conditions were investigated by Raman spectroscopy. The G band, especially Breit-Wigner-Fano (BWF) line, in the Raman spectra of DNA-SWNT hybrids strongly depends on the relative humidity. In the high humidity range above 55%, the BWF coupling increases with decreasing humidity. On the contrary, in the low humidity range below 55%, the BWF coupling decreases with decreasing humidity. The origin of such humidity dependence is discussed in the light of the behavior of the absorption of the water vapor on DNA in air. (c) 2006 Elsevier B.V. All rights reserved.