High-overtone induced chemistry of oxalic acid (OA) isolated in a low-temperature argon matrix was investigated using Raman spectroscopy. The Raman spectra of three conformers of OA are presented and discussed. Upon excitation of high overtone combination bands by 532 nm irradiation of the lowest energy cTc structure, the isomerization and unimolecular decomposition of OA were observed. Dissociation was induced presumably by absorption into the 5A(g) + B-u vibrational state of the OH stretching mode of cTc. The photodecomposition leads to the formation of CO, CO2, and H2O products. The experimental observations were supported by computational studies and vibrational anhar-monic calculations.