Abstract: Acetohydroxamic acid (AHA) is a new salt-free complexing agent which may be used in the reprocessing of spent fuel. The concentration of AHA in HNO₃ was analyzed by ultraviolet-visible spectrophotometry, and that of acetic acid which was produced by the hydrolysis of AHA was analyzed by ion chromatography. The stability of AHA in HNO₃, the effect of temperature and mono-methylhydrazine (MMH) on the stability of AHA and concentration of acetic acid were studied. Results show that the stability of AHA decreases with the increase of time and HNO₃ concentration, the effect of temperature on the stability of AHA in HNO₃ is obvious, and the stability of AHA in HNO₃ can be enhanced by MMH. At certain condition, AHA is of good stability in HNO₃ and can meet the technological requirement of the reprocessing of spent fuel.