The sublimation enthalpy and entropy of urea and its derivatives monomethylurea ( mmu), monoethylurea ( meu), monopropylurea ( mpu), dimethyl-1,1-urea (1,1- dmu), dimethyl-1,3-urea (1,3- dmu), and diethyl-1,3-urea (1,3- deu) were determined from the dependence of their vapour pressures on temperature. The vapour pressures were measured by the torsion-effusion method. The corresponding pressure against temperature equations are: urea, lg( p kPa ) = 10.30-4750( K T ) ; mmu, lg( p kPa ) = 10.72-4562( K T ) ; meu, lg( p kPa ) = 10.20-4496( K T ) mpu, lg( p kPa ) = 10.83-4608( K T ) ; 1,1- dmu, lg( p kPa ) = 11.13-4655( K T ) ; 1,3- dmu, lg( p kPa ) = 10.78-4454( K T ) ; 1,3- deu, lg( p kPa ) = 12.20-5047( K T ) ; where the errors associated with the slopes (±100) and intercepts (±0.18), (±0.30 for urea), were estimated.