A general phenomenon that electrospun polymer nanofibers self-assemble into honeycomb-patterned nanofibrous structures (HNFSs) is reported. We used electrospinning to produce charged polymer nano fibers, which were kept in liquid state (wet) on landing on the substrates by appropriatley controlling the electrospinning conditions. Driven by the competitive actions of surface tension and electrostatic repulsion, these charged wet nanofibers self-assemble into the HNFSs. Fabrication of the well-defined three-dimensional HNFSs was successfully demonstrated for three dimensional HNESs was successfully demonstrated for three different polymers, that is polyacrylonitrile, polyvinyl alcohol, and polyethylene oxide. The pore diameter of the obtained honeycomb structures spans a wide range from micrometers to over 200 mu m with depths as large as over 150 mu m. The pore walls are composed of uniaxially aligned polymer nanofibers.