Highly selective extraction of oxonium anions can be achieved by the new ligand, 2,2'-(methylimino)bis(N,N-dioctylacetamide) (MIDOA). MIDOA has a high solubility in n-dodecane, any types of diluents can be employed for the solvent extraction. The extraction using MIDOA was performed under the condition, HNO3 and n-dodecane, considering the chemical process of high-level radioactive liquid waste. It was obvious that the oxonium anions, like TcO4-, ReO4-, Cr2O72- MoO42-, and WO42-, are extracted, and the distribution ratios (D) decrease with increase of HNO3 concentration.