The adsorption of the urea molecule on the external surface of the B12N12 nanocage was investigated using density functional theory (DFT) calculations. Adsorption of urea on the nanocage releases energies of about -23.70 to -29.50 kcal/mol with a significant NBO charge transfer from the urea to the nanocage. It was also found that the urea molecule can be strongly chemisorbed on the surface of the nanocage with Gibbs free energies of -7.91 to -14.81 kcal/mol. The HOMO-LUMO gap of the nanocage does not change significantly upon urea adsorption, while the Fermi level is dramatically changed from -4.27 eV in the pristine nanocage to upper energies upon urea adsorption. The geometric structure, adsorption energy, solvation effect, charge transfer, and frequency analyses of the urea adsorption on the nanocage models showed that the urea molecule could be firmly adsorbed by the nanocage and the nanocage could be a potential efficient adsorbent for the adsorption of urea.