Molybdenum sulfides (Mo-S) have been the topic of current interest owing to the interaction between the hydrogen and unsaturated sulfur atoms. However, the correlation between the S concentration and structure, and relevant properties are not well understood. By using the first-principles calculations, we investigated the influence of S concentration on the structural stability, elastic and electronic properties of Mo-S sulfides. The formation enthalpy of Mo-S sulfides under high pressure is calculated. The previous unreported crystal structure of MoS with VS-type structure (space group: Pmcn, No. 62) is predicted. The convex hull indicated that MoS with hexagonal structure is more thermodynamic stability than that of other Mo-S sulfides. It is found that the structural stability is attributed to the charge contribution of S-3s state and S-3p state with increasing S concentration. The elastic properties of Mo-S sulfides are directly related to the S concentration. The bulk modulus of Mo-S sulfides decreases linearly with increasing S concentration. Finally, it is concluded that Mo-S sulfides exhibit metallic behavior except for MoS2. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.