In order to design a recovery process of phosphorous acid from the wastewater of electroless nickel-plating, the extraction of phosphorous acid in the aqueous solution with tri-n-octylamine in toluene was carried out using a vibration type continuous extractor, which has multiple vibration disks in a cylindrical tube. The effects of the initial concentrations of the extractant and phosphorous acid and the mean residence time of both solutions in the extractor on the extraction rate of phosphorous acid were measured under various conditions. The experimental results correlated to the complete mixing flow of both fluids in the extractor were analyzed based on the apparent rate equation of (2.0, 2.0)th orders for the acid and the amine. The calculated results for each frequency number of the vibration plates were in good agreement with the experimental results.Key words: extraction rate, phosphorous acid, vibration type extractor, electroless nickel-plating, tri-n-octylamine 電解ニッケル,トリ -n-オクチルアミン 1 吉玉精鍍株式会社研究開発部 2 宮崎大学工学部物質環境化学科 平成 18 年 9 月 13 日受理