A thermochemical study of benzoxazole and benzothiazole was carried out by sublimation calorimetry (using a Tian-Calvet calorimeter equipped with a Knudsen effusion cell) and differential thermal analysis (DTA).Delta(sub)H(m)(0) (298.15 K)=(69.48+/-0.44) kJ mol(-1) for benzoxazole and Delta(vap)H(m)(0) (298.15 K)=(60.92+/-0.52) kJ mol(-1) for benzothiazole.Delta(fus)H(m)=(15.92+/-0.15) and (11.95+/-0.08) kJ mol(-1) for benzoxazole and benzothiazole, respectively.T-triple point=(302.90+/-0.01) acid (275.53+/-0.10)K for benzoxazole and benzothiazole, respectively.These experimental results allowed us to determine qualitatively and quantitatively the intermolecular interactions and to discuss the relative stability of the two molecules. A study of the relative stability of some related compounds has also been realized.