Boron nitride (BN) nanocage clusters of B24N24 were synthesized and detected by laser desorption time-of-flight mass spectrometry. The B24N24 clusters consisted of 4-, 6- and 8-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. The electronic structure showed a bandgap energy of 4.9 eV, which is smaller than that of B36N36 cluster. (C) 2003 Elsevier B.V. All rights reserved.