Phonon properties of boron nitride nanotubes (BNNTs) were investigated using Raman spectroscopy at different temperatures and new sp(3)-bonded BN vibrations were identified. The Raman peak of the E-2g mode of BNNTs is found to be downshifted and broadened compared to that of hexagonal BN at the same temperature. By increasing the temperature, the energy of the E-2g mode and the sp(3)-bonding mode are downshifted, with the temperature coefficients being -0.010 and -0.069 cm(-1)/K, respectively. We attribute this downshifting to anharmonic effects as well as the elongation of the B-N bond in BNNT structures with increasing temperature. (C) 2014 The Japan Society of Applied Physics