The chemical degradation of curcumin (CU) in aqueous solution and on silver nanoparticles was studied by means of ultraviolet (UV)-visible absorption and surface-enhanced Raman (SERS) spectroscopy at different pH levels and upon light irradiation. CU undergoes a chemical degradation in aqueous solution mainly when the pH is increased. The CU degradation is catalytically enhanced in the presence of Ag nanoparticles. In general, CU degradation implies two steps: (1) the breakdown of the interring chain connecting the two CU aromatic side rings, producing smaller phenolic compounds rich in carboxylate groups, and (2) polymerization of the resulting phenolic products, giving rise to phenolic polymeric products. The degradation-polymerization mechanism can be modulated depending on the experimental conditions. The chemical photoproducts resulting from the visible light irradiation are similar to the polycatechol products obtained when catechol is adsorbed on Ag nanoparticles.