We report a new quasi-one-dimensional compound KMn6Bi5 composed of parallel nanowires crystallizing in a monoclinic space group C2/m with a = 22.994(2) angstrom, b = 4.6128(3) angstrom, c = 13.3830(13) angstrom and beta = 124.578(6)degrees. The nanowires are infinite [Mn6Bi5](-) columns each of which is composed of a nanotube of Bi atoms acting as the cladding with a nanorod of Mn atoms located in the central axis of the nanotubes. The nanorods of Mn atoms inside the Bi cladding are stabilized by Mn-Mn bonding and are defined by distorted Mn-centered cluster icosahedra of Mn-13 sharing their vertices along the b axis. The [Mn6Bi5](-) nanowires are linked with weak internanowire Bi-Bi bonds and charge balanced with K+ ions. The [Mn6Bi5](-) nanowires were directly imaged by high-resolution transmission electron microscopy and scanning transmission electron microscopy. Magnetic susceptibility studies show onedimensional characteristics with an antiferromagnetic transition at similar to 75 K and a small average effective magnetic moment (1.56 mu(B)/Mn for H parallel to b and 1.37 mu(B)/Mn for H perpendicular to b) of Mn from Curie-Weiss fits above 150 K Specific heat measurements reveal an electronic specific heat coefficient gamma of 6.5(2) mJ K-2(mol-Mn)(-1) and a small magnetic entropy change Delta S-mag approximate to 1.6 J K-1(mol-Mn)(-1) across the antiferromagnetic transition. In contrast to a metallic resistivity along the column, the resistivity perpendicular, to the column shows a change from a semiconducting behavior at high temperatures to a metallic one at low temperatures, indicating an incoherent-to-coherent crossover of the intercolumn tunneling of electrons.