The optical-response extraction of An(III) with an azo compound, his(2,2'-dipyridyl-6-yl)diazene (BDPDA), was studied. The distribution ratio of Au was increased by the configuration change of BDPDA from (rams to cis under UV irradiation (340 nm); however, the distribution ratios under UV irradiation were less than 3 tunes those under VIS irradiation (465 nm). For further improvement of optical-response extraction, the synergistic extraction of Au using octanoic acid as a synergist was tested. Octanoic acid was coordinated mainly with the complex of Au and cis-BDPDA, and effectively enhanced the hydrophobicity of the complex. The distribution ratio of Au under the UV irradiation increased with increasing the concentration of octanoic acid in the organic phase. In the presence of 3 mol/L, octanoic acid. the distribution ratio under the UV irradiation reached up to 10 times that under the VIS irradiation.