Catalyst-free growth of boron nanoribbons was observed by pyrolysis of diborane at 630-750 degreesC and similar to200 mTorr in a quartz tube furnace. Nanodiffraction analysis indicates the nanoribbons are single crystal alpha-tetragonal boron. TEM images show the nanoribbon is covered by a 1-2 nm thick amorphous layer. Elemental analysis by EELS, EDX, and XPS shows the nanoribbons consist of boron with small amounts of oxygen and carbon. Infrared and Raman spectra are also reported.