TiN whiskers were synthesized using K₂TiF₆ as a starting material and B₂O₃ as an additive. The largest amount of TiN whiskers was deposited when 1mmol of B₂O₃ was placed in a graphite boat (1), a mixed powder containing K₂TiF₆ and B₂O₃ was placed in another boat (2), and then they were both heated at 1400°C for 10h. B₂O₃ evaporated was considered to accelerate the thermal decomposition of alumina tube, investigating the effect of addition of B₂O₃. Scanning electron microscopy and transmission electron microscopy of the obtained whiskers revealed that most of the whiskers were square prismoidal shaped and some were hexagonal or octagonal prismoidal shaped. The square and octagonal prismoidal whiskers grew in the ‹100› direction and the hexagonal prismoidal whiskers grew in the ‹111› direction. As in the case of whiskers synthesized from other materials, the tensile strength of the whiskers increased with decreasing cross-sectional area of the whiskers, indicating the size effect.