Thin, amorphous boron-carbon films are deposited at low temperature (400–600 °C) by thermally activated CVD using the organoborane triethylboron (TEB) as a single precursor. Two different carrier gases are tested. At 600 °C, using argon as the carrier gas, the deposition rate is close to 1 µm h−1. The film has a density of 2.14 g cm−3 with a B/C ratio of 3.7. When hydrogen is used as the carrier gas, the film density is 2.42 g cm−3, the B/C ratio 4.6, and the deposition rate 0.35 µm h−1. The hydrogen content in the films is about 3–4 at.-%, regardless of ambient conditions during deposition, and varies only with the deposition temperature. In addition, both the film composition and the film density are found to vary significantly with the deposition temperature and the atmospheric conditions. Based upon these results, a deposition mechanism for the growth of boron-carbon films from TEB, where the TEB molecule is decomposed to BH3 and hydrocarbons, is suggested.