We report herein investigation on crystallization of amorphous molybdenum sulfide a-MoS x induced by electron and laser beam resulting in formation of crystalline molybdenum disulfide c-MoS2. This crystallization occurred in situ during transmission electron microscopic and Raman analyses of a-MoS x material. It was also found that a-MoS x to c-MoS2 phase transformation was not fully beneficial for H2-evolving catalytic performance. c-MoS2 showed better robustness but significantly lower catalytic performance. Furthermore, c-MoS2 was less tolerant to oxidation stress, as the one caused by photogenerated holes within the light harvester, compared with a-MoS x catalyst. Thus, a-MoS x is a better candidate for implementation within photocatalysts for overall solar water-splitting application.