Abstract The signals of anionic sulfur clusters are intense in the mass spectrum of sulfur clusters generated in direct laser vaporization. We have acquired numerous isomers of sulfur clusters by means of the B3LYP DFT method. According to total energies, the most stable S n − ( n=3–13) isomers are predicted. The helical S n ( n=14–20) structures are also calculated. Most of the anionic clusters are with chain configurations; the ring clusters with threefold atom(s) are higher in total energy. The most stable forms of isomers, from S 9 − to S 13 −, show helical configurations that are completely different from those of the corresponding neutral and cationic clusters.