The surface reaction and adsorption behavior of phenylacetylene adsorbed on a gold electrode were studied by means of in situ electrochemical surface-enhanced Raman spectroscopy (SERS). The results showed that phenylacetylene would become phenylacetylide and it was perpendicular with respect to the gold surface. The adsorption mode of phenylacetylide did not prominently change in a certain potential region. The change in the spectral features of SER spectra detected at more negative potential revealed that an addition reaction occurred with the carbon-carbon triple bond of phenylacetylene. Compared with SERS of styrene on a gold electrode, during the potential region of －0.6 V to －1.2 V, there might be styrene produced on the surface of the electrode. Finally, it would be reduced to ethylbenzene.