A kinetic reaction model for thermal decomposition of urea is presented. Systematic thermogravimetric analyses of urea and its most important byproducts, such as biuret and cyanuric acid, are performed to gain the main reactions and their rates. Gaseous products are analyzed and the concentrations of solid products are determined. The reaction scheme, as well as the kinetic parameterization, is validated at different heating rates. The proposed kinetic reaction model matches all performed thermogravimetric analyses and it is also able to reproduce changes in the measurement conditions, such as differences of crucibles geometry or variations of the initial sample mass.