Using density functional theory, we investigate the adsorption behavior of CO, NH3, and NO molecules on monolayer Si2BN. The energetically favorable structural configurations along with their adsorption energies, charge transfers, and electronic properties are discussed. The CO and NH3 molecules show physisorption with moderate adsorption energies, whereas the NO molecule is subject to chemisorption. We further calculate the current–voltage characteristics using the non-equilibrium Green's function formalism. Significant anisotropy is observed for the armchair and zigzag directions, consistent with the anisotropy of the electronic band structure. Pronounced enhancement of the resistivity upon gas adsorption indicates that monolayer Si2BN is promising as gas sensing material.