Nanocrystalline boron phosphide (BP) has been prepared by the reaction of PCl3 with NaBH4 at 600degreesC in an autoclave. The X-ray powder diffraction patterns can be indexed as cubic BP with the lattice constants of a = 4.53 Angstrom. The transmission electron microscopy (TEM) image shows particle morphology, with average size of 10 nm for the powders. The selected area electron diffraction (SAED) patterns confirm the prepared BP.