Condition-dependent transformations between hydroximic acids and thioacetic acid were achieved. Using NH4HCO3 in the ethanol solvent, efficient N–O bond cleavage of hydroxamic acids occurred to afford primary amides with high functional group compatibility. The reaction was switched to O-acylation when NEt3 and H2O were used as the base and solvent, respectively. These facile transformations could be scaled up to the gram level smoothly. Preliminary mechanistic studies suggested that the N–O bond cleavage involves a cascade process of acylation/reduction.