An infrared absorption spectrum of formic acid dimer (HCOOH), in the C-H stretching region has been observed in a supersonic jet by cavity ring-down spectroscopy. In total six vibrational bands have been identified in the region 2800-2950cm(-1), and the center frequency and relative intensity for each of them, as well as its tentative assignment, has been cm determined. Comparison with previous studies has shown that there is a discrepancy with regard to the assignment of the O-H stretching band.