Ab initio SCF MO calculations were performed on 2,3-butadien-1-ol and the optimized geometries obtained by the use of the STO-3G and 3-21G basis sets. The single-point calculation using the 4-31G basis was also applied to the molecule. The optimized geometry is in good agreement with the observed one which was estimated from analysis of the microwave spectra. The relative stability of the several rotational isomers of the molecule, if they exist, is discussed in the light of the results of the present calculations. The main factor to stabilize the form was explained on the basis of the electronic structures. The variation of the bond angle α(CCO) due to the rotational isomerism is analyzed.