The NOx gases which are released from diesel vehicles can be reduced to N-2 gas with selective catalytic reduction (SCR) reactions. The yield of these reactions are majorly related to the reducing agent. Both urea and its' decomposition/hydrolysis compounds which are isocyanic asid (HNCO) and ammonia (NH3) can be used SCR reactions. Therefore, urea is an attractive reducing agent recently. Ag/Al2O3 catalysts have an important role for NOx reduction. The decomposion and hydrolysis compounds of urea on the %1 Ag/Al2O3 and %2 Ag/Al2O3 catalysts which are prepared by sol-gel method were investigated by using FTIR. The experimental studies were carried out between 100-400 degrees C temperature in the presence of helium. As a result of the analyses of FTIR spectra, NH3, NH4+, -CNO, melamine and CO2 were dedected as the decomposition and hydrolysis compounds of urea on the catalysts. Besides that, OH, CH, NH and C=O stretching vibration bands were also observed. NH4+ compound was not observed at any temperature on the % 1 Ag/Al2O3 catalyst however, it was observed at the temperatures of 100 and 250 degrees C on the % 2 Ag/Al2O3 catalyst. Ammonia, which is a decompositon and hydrolysis compound of urea, was observed on both catalysts at all temperatures and times. Isocyanate (-CNO), which is a decompositon compound of urea, gave its most intensive peak at the temperature of 200 degrees C on %1 Ag/Al2O3 catalyst and at the temperature of 250 degrees C on %2 Ag/Al2O3 catalyst.