Hydrophobic effects on multivalent-salt-induced self-condensation of a single polyelectrolyte chain such as DNA are investigated through a multiscale coarse-grained simulation based on density functional theory. We show that the water-mediated hydrophobic effect that was enhanced by hydration of multivalent salts plays an essential role in self-condensation of DNA. The self-condensation is interpreted as an entropy-driven compaction due to the hydration entropy gain. (C) 2009 American Institute of Physics. [doi:10.1063/1.3256982]