We studied the excitonic states of KP15 nanowires, which have high carrier mobility and in-plane anisotropic electrical and optical properties. Power, thickness, and temperature-dependent photoluminescence (PL) measurements were carried out. We found two neutral exciton emissions from KP15 nanowires. The high energy emission (1.83 eV) seems to have been produced by the surface state, and the lower one (1.67 eV) may have been produced by the original crystal structure of KP15. The KP15 nanowires also exhibited a large exciton binding energy (98 meV), which is one order of magnitude greater than those of common semiconductors. These properties make KP15 nanowires an interesting material for electrical and optical applications.