Molybdenum sulfide is actively being researched as a potential non-precious alternative to platinum in electrocatalytic water splitting. It is known that MoS2 exhibits significant hydrogen evolution reaction (HER) catalytic activity in acidic media. The precise mechanism of action is not yet known, but it is commonly thought that the low hydrogen adsorption energy (ΔGH = 0.08eV [1]) facilitates easy hydrogen adsorption and desorption. The rate of the Volmer (adsorption) step of the hydrogen evolution reaction increases, and either the Heyrovsky or Tafel (recombination) steps become limiting. The theory is confirmed by researchers reporting Tafel slopes of 40 – 50 mV dec-1 for MoS2 layers, obtained by various methods [2]. In this study we investigated the electrodeposition of non-stoichiometric MoS2-x from a common molybdenum and sulfide precursor – tetrathiomolybdate (TTM/MoS42-). The material‘s HER electrocatalytic activity was evaluated by linear sweep polarization in 0.5 M H2SO4 to determine overall catalytic activity and Tafel slopes. In addition, chronopotentiometric measurements at working current of -40 mA cm-2 were used to evaluate the mid to long-term stability of the layers. It was found that the films obtained at higher deposition potentials (the deposition time was 10 minutes for all obtained films) usually yielded better catalytic activity (see Fig. 1). Thus, the overpotential increased from 260 mV to 176 mV (at - 10 mA cm-2 HER current) for samples, deposited respectively at -0.9 V and -1.2 V vs Ag/AgCl. However, the Tafel slopes decreased from 50.8 mV dec-1 to 61.3 mV dec-1 for the same samples, signifying decreased activity of catalytic sites. The layer deposited at -1 V had a Tafel slope of 43 mV dec-1 and could be proposed as the optimal conditions for deposition.