The alkaline hydrogen evolution reaction (HER) plays a key role in photo(electro)catalytic water splitting technologies, particularly in water-alkali electrolyzers. Unfortunately, although transition metal dichalcogenide (TMD) materials, especially MoS2 and MoSe2, are considered efficient, Earth-abundant catalysts for the HER in an acidic electrolyte, they are much less effective under high pH conditions due to a sluggish water dissociation process (Volmer-step) and strong adsorption of the OH- intermediate on their surfaces. Herein we show a novel synergetic effect obtained by tailoring the S/Se ratio in Mo(SxSe1-x)2 alloys. We were able to influence the metal oxidation state and d-band to optimize the catalytic sites for H⋯OH dissociation and OH- desorption while maintaining favourable M-H energetics. The Mo(SxSe1-x)2 (x = 0.58) catalyst exhibited high performance with an onset potential of -43 mV in 0.5 M KOH, i.e., ∼3 and ∼4-fold less than that for MoSe2 and MoS2, respectively. The results obtained in the current study have implications for the rational design of cost-effective electro-catalysts for water reduction based on TMD alloys.