Abstract: The Hydrogen evolution reaction (HER) is an important process during electrocatalytic water splitting for hydrogen energy generation. Two dimensional (2D) MoS2 has been considered as a promising alternative to Pt-based catalysts in the hydrogen evolution reaction. However, the highest contribution for the catalytic activity of 2D-MoS2 is from its edge sites, this in turn leaves many in-plane domains useless. In this study, the effect of single atom metal (Pt, Ni and Pt-Ni) doping on HER catalytic activity of in-plane atoms was investigated using density functional theory calculations. The Gibbs free energy of adsorbed hydrogen on pristine MoS2 decreased from 1.86eV to -0.08eV in PtNi co-doped MoS2. This demonstrates enhanced catalytic activity of MoS2 due to atomic doping. The enhanced catalytic activity may also be attributed to the observed changes and increase in the density of electronic states near the Fermi energy level