The gamma-irradiation method was used successfully to prepare; nanocrystalline ZnS in sphalerite structure at room temperature. Sodium thiosulfate, thiourea and mercaptoethanol were used as sulfur sources. The products obtained from irradiated solutions containing zinc ions and different sulfur sources are all sphalerite phase. The TEM images indicate that the product from mercaptoethanol is in best dispersion, and that from sodium thiosulfate aggregates most heavily. The possible mechanisms of the formation of zinc sulfide in different systems are proposed.