This Letter studies intensity relation between IR-UV doubly resonant sum-frequency vibrational spectra (DR-SFVS) and antisymmetric resonant vibrational Raman scattering, and gives an approximate expression of their intensity ratio. Based on the intensity ratio expression and the related experimental data of IR and antisymmetric resonant vibrational Raman spectra, hypothetical DR-SFVS of ferrocytochrome c has been sketched. The experimental investigation on IR-visible DR-SFVS of ferrocytochrome c may be a test of the related theory. (c) 2008 Elsevier B.V. All rights reserved.