The melting, vaporization and thermal decomposition of monoethyl-, 1,3-diethyl-, monophenyl-, 1,3-diphenyl-urea were investigated by means of TGA and DSC measurements together with evolved products analysis by I.R. spectrometry. I.R. spectra allowed to identify isocyanate, amine and trimer among the compounds coming from the thermal treatment. DSC data seem to indicate hydrogen bonds are determinant for the enthalpy of vaporization of these derivatives of urea.