In situ deposition of catalysts are drawing attention to the liquid/liquid interfaces by using raw materials for the energy conversion reactions such as hydrogen evolution and oxygen reduction. Herein, in situ generation of amorphous molybdenum sulfide on reduced graphene oxide (rGO/MoSx) is investigated in the hydrogen evolution reaction (HER) by decamethylferrocene electron donor at the liquid/liquid interfaces by using (NH4)2MoS4 and graphene oxide precursors in the aqueous phase. rGO/MoSx catalyst shows better catalytic activity than the uncatalyzed reaction and free-MoSx, which increase the HER rate 57- and 1.7-fold, respectively. The enhanced catalytic activity of rGO/MoSx catalyst is related to the increased surface area, active sites and conductivity of rGO. The catalytic activity of rGO/MoSx are examined by four-electrode voltammetry and also two-phase reactions. The obtained rGO/MoSx catalyst are characterized in detail by structural and morphological techniques.