Density functional theory combined with the non-equilibrium Green’s function formalism is used to study the adsorption and gas-sensing properties of H2 gas molecule on pristine and doped ZnO nano-ribbons (NRs). Substitutional doping of oxygen site with C, N and F have been tested versus adsorption of H2 molecule and other molecules (e.g., N2, O2, H2O, H2S). The results of relaxation show chemisorption to occur only on C-and N-doped samples. While all these molecules exhibit chemisorption on C-doped ZnO-NR, only H2 and O2 molecules are chemisorbed on N-doped ZnO-NRs. The chemisorption of O2 is associated with the breaking of one π-bond and thus desorption in reversal process is plausible. However, the chemisorption of H2 is associated with a complete dissociation and introduces donor states into the gap (i.e., it plays a role of n-type dopant) and consequently enhancing the conductivity. These characteristics made N-doped ZnO-NRs have high sensitivity and selectivity towards the detection of H2 gas. Furthermore, the calculated IV-curves have paved the way for estimating the sensitivity and consolidated our results. Since the change of conductance is one of the main outputs of sensors, our findings will be useful in developing Hydrogen-based solid-state sensors.