The interactions between boron carbide (BC) nanocluster of B16C16 and H2O, NO2, CO, and CH4 small molecules were investigated by using density functional theory (DFT) computations to exploit the structural and electronic properties of the adsorbate/cluster complexes. The calculated adsorption energies of the most stable states are -16.6, -0.17, -1.28, -0.18 eV for NO2, CO, H2O, and CH4 molecules, respectively. Meanwhile, the interactions between CO and CH4 molecules and the cluster induce dramatic changes to the cluster electronic properties so that the molecular orbital (HOMO/LUMO) gap of cluster decreased its original value. It was shown that the phenomenon leads to an increment in the electrical conductivity of the cluster at a definite temperature. Furthermore, it is revealed that the adsorptions of NO2 and H2O molecules have no significant effects on the electronic properties of the cluster. Thus, this work suggests that the investigated B16C16 nano-cage could work as a selective gas sensor device towards CO, CH4, NO2 and H2O molecules.