We employ density-functional theory within the generalized-gradient approximation to investigate infinitely long double-wall bismuth nanotubes (DWBiTs). It is found that the interwall interaction has an important role in the stability of DWBiTs and different effects on band structures of armchair and zigzag DWBiTs. Armchair DWBiTs are more sensitive to interwall interaction than zigzag DWBiTs. All DWBiTs are found to be semiconductors with band gaps smaller than that of single-wall tubes. This indicates that there will be a semiconductor-metal transition with the increase of the wall thickness of bismuth nanotubes as recently observed in experiments. (C) 2008 Elsevier B.V. All rights reserved.