We perform a systematic study on the geometry, stability, nature of bonding, and potential energy surface of low-lying isomers of planar and cyclic BnN2 (n = 1−6) at the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level. BnN2 (n = 2−4) clusters are structurally similar to pure boron clusters. The evolution of the binding energy per atom, incremental binding energy, and second-order difference of total energy with the size of BnN2 reveals that the lowest energy isomer of B3N2 has high stability. B5N2 and B6N2 possess π-aromaticity according to Hückel (4n + 2) rule. The aromaticity of some isomers of B4N2 and B6N2 is examined based on their valence molecular orbitals. At the CCSD(T)/6-311+G(d)//B3LYP/6-311+G(d) level, several B2N2, B3N2, B4N2, and B5N2 isomers are predicted to be stable both thermodynamically and kinetically, and detectable in future experiments. © 2013 Wiley Periodicals, Inc.