The adsorption of HNCO has been investigated on Ag/SiO2 catalyst by means of FTIR spectroscopy. Adsorption of HNCO on the reduced sample at 190 K produced an absorption band at 2,170 cm(-1) attributed to NCO bonded to Ag. Annealing the adsorbed layer under continuous degassing, the 2,170 cm(-1) band gradually attenuated and at the same time a spectral feature at 2,300 cm(-1) supercript stop due to Si-NCO developed. From these spectral changes it was inferred that NCO bonded to Ag spilt over onto silica.