A simple solution-phase route was developed for the large-scale synthesis of self-organized, closely packed ultralong single crystalline Se nanowire superstructures with diverse morphologies and macroscopic dimensions even extending over several millimeters. The hierarchical architectures of self-organized Se nanowires were formed by reducing H2SeO4 with a bisubstituted aniline, such as 3,5-dimethoxyaniline, 2,5-dimethoxyaniline, 2,6-dimethoxyaniline, and 2-methoxy-5-nitroaniline under solvothermal conditions. Scanning electron microscopy studies show 100% morphological yield and morphological uniformity of the self-organized hierarchical architectures. Based on the dependence of the Se nanostructures on the synthetic conditions, especially the molecular structures of reductants and solvent, we proposed a plausible mechanism to account for the formation of the distinctive morphologies of the self-organized nanowire architectures. The field emission characteristics of the Se nanowires synthesized using 2,6-dimethoxyaniline and 2-methoxy-5-nitroaniline as the reductants are studied. These well-aligned Se nanowires show very low turn-on field (Eto) and threshold field (Ethr) as well as high emission current densities under low applied electric fields, which are superior to most of the one-dimensional (1D) nanostructures reported previously, due to their exceptional aspect ratios (>20 000) and sharp tips in combination with the nature of low band gap and high conductivity of Se. Furthermore, the Se nanowire emitters exhibit good emission current stability with small fluctuations (typically, less than 3%) over a period of 1000 min.