Nivalenol, a highly poisonous mycotoxin, and its possible tautomers have been considered theoretically by RHF/6-31G/d,p) and B3LYP/6-31G(d,p) calculations together with a semi-empirical PM3 method. The calculations revealed that some of the tautomers are more stable and exothermic than nivalenol. The calculated IR spectra as well as some geometrical and physicochemical properties of the structures considered have been presented.