The establishment of cost-effective photocatalytic system based on earth-abundant materials is crucial for the practical utilizations of solar energy. To achieve this goal, it is highly desirable to employ photosensitizers and catalysts that are both derived from earth-abundant materials. Herein, we report an efficient noble-metal-free system by integrating the above two components. We found that functional MoSx nanoparticles can be obtained with an in situ photoreduction manner during photocatalytic reactions in the presence of inexpensive organic sensitizers. The thus-obtained MoSx catalysts demonstrated quite high efficiency for catalyzing H-2 evolution under visible light. The factors influencing the performance of the photocatalytic system was investigated and a two-step reaction mechanism was proposed. The concept of in situ formation of hydrogen evolution catalyst paves the way for investigating biomimetic molybdenum sulfide catalysts for photocatalytic H-2 production in systems without the presence of noble metals. (C) 2013 Published by Elsevier Inc.