This Letter introduces a systematic development of a quantitative vibrational force field (FF) capable of modeling vibrational spectra of cobalt corrinoids (B-12 derivatives). The scaled quantum mechanical (SQM) method is used to refine density functional theory (DFT) based force constants calculated at the B3LYP level of theory. The reliability of the DFT-SQM FF for cobalt corrinoids is tested on a six-coordinate methylcobalamin Im-[Co-III-corrin]-CH3 model. It is shown that the computed frequencies and Raman intensities permit detailed vibrational assignment. This analysis illustrates the utility of DFT-SQM FF in making detailed connections between the structure of cobalt corrinoids and their vibrational spectra,