Rechargeable cells with a sulfur cathode, a lithium anode and a nonaqueous electrolyte operating at ambient temperature have been extensively studied as a possible application of sulfur combined with nonaqueous solvent. However, the behavior of the chemical species formed by the reduction of sulfur with alkali metals in nonaqueous solvent has not yet been clarified. In this report, sulfur is reduced in tetrahydrofuran (THF) by alkali metals (M : Na, K, Li and Cs), by anthracene radical anions or by diphenylethylene dimer dianions with alkali metal counter cations mainly under the experimental condition of [S-s]/[M] > 0.25. The system produced by the reduction is the yellow solution consisting of polysulfide dianions (S-m(2-), m > 1) and radical anions (S-n(radical anion), n > 1) which changes into a blue solution by the addition of hexamethylphosphoric triamide with a much higher polarity than THF. The influence of the kind of alkali metal, the temperature and the addition of solvents such as crown ether on the behavior of the chemical species formed are examined by ultraviolet (uv)-visual electronic spectra, electron spin resonance (ESR) spectra and Raman spectra measurements. In addition, gamma-irradiation with Co-60 was carried out to reduce sulfur in glassy solid 2-methyl-THF at -196 degrees C. Furthermore, the reaction between the yellow solution and aliphatic bromide is investigated. As a result, it is revealed that the yellow species is S-4(2-), the blue species is S-3(radical anion) and several polysulfide dianions and radial anions are in a state of equilibrium.