Adsorption of chlorine molecule (Cl-2) on the Zn12O12 nano-cage has been analyzed using density functional theory. It has been shown that the Cl-2 molecule is strongly adsorbed on the cluster via two mechanisms including chemisorption and dissociation with Gibbs free energy changes in the range of -0.36 to -0.92 eV at 298 K and 1 atm. These processes also significantly change the electronic properties of cluster by decreasing its HOMO/LUMO energy gap and increasing the work function. The Fermi level shifts towards lower energies upon the interactions between Cl-2 and the cluster, resulting in raised potential barrier of the electron emission for the cluster and hence avoiding the field emission. The Zn12O12 cluster is transformed to a p-type semiconductor substance upon the Cl-2 dissociation. We believe that the obtained results may be helpful in several fields of study such as sensors, catalysts, and field emission investigations. (C) 2012 Elsevier B.V. All rights reserved.