The microwave spectrum of the sugar alcohol 1,2-propanediol (CH 3 CHOHCH 2 OH) has been measured over the frequency range 6.5–25.0GHz with several pulsed-beam Fourier-transform microwave spectrometers. Seven conformers of 1,2-propanediol have been assigned and ab initio electronic structure calculations of the 10 lowest energy forms have been calculated. Stark effect measurements were carried out on several of the lowest energy conformers to provide accurate determinations of the dipole moment components and assist in conformer assignment.