One of the main loss factors in the optical fibers fabricated by the vapor phase axial deposition process is at present residual OH ions which are originated mainly from an oxy-hydrogen flame. Residual OH ions show an influence on loss increase, especially, in the long wavelength region. OH-ion behaviors in the porous perform, transparent perform and drawn fibers are studied with use of an infrared spectroscopy and fiber transmission measurement. In order to realize low OH content VAD fibers, the dehydration effect of halide vapor on the porous perform is investigated experimentally. Dehydration effect of thionyl chloride on the porous perform is studied by various heat treatment temperature. As a result, residual OH ion content in the drawn fiber was reduced from 30 ppm to 20 ppb and the attained minimum loss of dehydrated fiber was 0.5 dB/km and 0.28 dB/km at 1.3 µm and 1.6 µm wavelengths, respectively. Present investigation clarified that the VAD fibers are applicable to an optical transmission system in the long wavelength band. We compare the loss peak values at the wavelengths of 1.39, 1.24 and 0.95 µm among several optical fibers fabricated by different method. Especially, the VAD fibers dehydrated with SOC12 show abnormal peak ratios at the wavelengths.