The transport properties and I-V characteristics of boron-carbon and boron-nitride quantum dot devices are investigated by first principles method. The results of the B-C and B-N devices consisting of the same number of atoms have significant differences. There is large density of states near the Fermi energy for B-C device. A wide gap in the density of states of B-N device exists and the Fermi energy lies in the gap. The B-C device reveals metal property and the B-N devices appear as semiconductors.