Ab initio first-principles calculations are carried out to investigate Ti (Sc)-decorated two-dimensional boron-carbon-nitride (BC 2 N) sheets for their application as hydrogen storage materials. The results show that with four H 2 molecules attached to per metal atom the Ti (Sc)-decorated BC 2 N can store up to 7.6wt% (7.8wt%) of hydrogen in molecular form. The Kubas interaction and the polarization mechanism lead to the adsorption energy within the range of 0.4–0.56eV/H 2 (0.13–0.27eV/H 2 ), which is suitable for ambient temperature hydrogen storage.