Extraction of succinic acid and acetic acid by tri-n-octylamine (TOA) was studied under various pHs of their aqueous solutions. For the extraction of both acids, the loading values decreased with increasing values of pH. In the extraction of acetic acid, the sharp decrease in loading values with increasing pH began at higher values than that of succinic acid extraction due to its higher pK(A) value. Based on the different extractability for succinic acid and acetic acid with pH, the selective removal of acetic acid from succinic acid and acetic acid aqueous mixture was carded out. After three successive extraction by 0.25 mol kg(-1) TOA dissolved in I-octanol at pH 5. 1, the large amount of acetic acid from aqueous acid mixture could be removed. (C) 2004 Elsevier B.V. All rights reserved.