Abstract: Acetohydroxamic acid (AHA) is synthesized by the method of hydrochloric hydroxylamine reaction with acetic ether in alcohol water medium and its structure is characterized by element analysis, IR, MS, et al. The stability constants of AHA complexes with Pu(Ⅳ) and Np(Ⅳ) have been determined in 1 mol/L nitric acid solution by TTA extraction method. The value of stability constant β 1 is 5 3×10 12 and 6.1×10 11 , respectively.