In the present work, we studied thiram on silver surface by SERS. Investigations of disulfides with SERS revealed that the molecules undergo a surface reaction on silver, namely easy cleavage of the S-S bond. We believe that the two S atoms of resonance formed from the thiram may be chemisorbed strongly on Ag sol. This resonance form adheres perpendicularly to the Ag surface via the two S atoms, since the ${delta}(CH3)$ and n (CN) mode perpendicular to the surface showed strong enhancement. The important roles of halide anion adsorption have been discussed and the pH effects of thiram on Ag sol in acidic, neutral, and alkaline conditions were examined.