Urea thermolysis and isocyanic acid hydrolysis over three kinds of zeolites are investigated experimentally and the main decomposition products, NH3 and HNCO, are focused on. The results gained using thermogravimetric analysis with heating rates of 2 degrees C/min from 50-500 degrees C show NH3 releases mainly in 133-250 degrees C and the main thermal product above 250 degrees C is HNC. NH3 release process appears double-peaked while HNCO triple-peaked. Zeolites shift urea decomposition to lower temperature and shorten the process. The experiments of urea thermolysis over zeolites were done in the fixed reactor at programmed temperature and constant temperature. Although zeolites enhance the production of both NH3 and HNCO, the yield ratio of NH3 increases to 1.1 from 0.9 when adding zeolites but the yield ratio of HNCO is always below 0.8. Under zeolites's catalytic effect, the peak of NH3 release and the second peak of HNCO release become stronger. Moreover, zeolites can result in the HNCO peaks integrating into a stronger peak at 500 degrees C. The total yield of NH3 and HNCO increases about 0.1-0.2 with zeolites and the catalytic effect is more obvious at low temperature. In the experiment of thermolysis with a urea-water spray, over 96% urea could decompose to NH3 and HNCO when the temperature is over 550 degrees C and the residence time is more than 1.0 s. Zeolites show good catalytic performance on HNCO hydrolysis to NH3 and the conversion of HNCO to NH3 increases with increasing temperature and reaches above 80% at 250 degrees C and can touch 100%. The catalytic effect on urea thermolysis and HNCO hydrolysis decreases in the order H-Y > H-beta > H-ZSMS, which might be due to the amount of acidic sites on the catalysts. The apparent activation energy of the hydrolysis reaction is so low that the overall hydrolysis reaction rate on catalysts is mainly determined by external and internal mass-transfer limitations.