Frequency fluctuation of the NO stretching mode of the sodium nitroprusside, [Fe(CN)(5)NO](2-), in H2O and D2O was studied by three-pulse infrared photon echo spectroscopy. It is found that the time-correlation function of the frequency fluctuation of this mode is characterized by time constants similar to those of the triply degenerate T-1u mode of the CN stretching of [Fe(CN)(6)](4-), showing that the vibrational frequency fluctuation is not dominated by the time-dependent anisotropic solute-solvent interaction.