Effects of hydrostatic pressure have been investigated in a quasi-one-dimensional (quasi-1D) mixed-valence (MV) gold complex [AuCl(DBS)][AuCl3(DBS)] (DBS=dibenzylsulfide) by means of high pressure Raman spectroscopy up to similar to13 GPa at 300 K We have observed pressure-induced suppression of a Raman-active Au-Cl stretching mode, indicating a precursor of the pressure-induced phase transition from the MV state to a single-valence (SV) state.