Fundamental studies were carried out for the separation and recovery of acid from the waste etching solution discharged from the silicon wafer manufacturing industry by using solvent extration. 2-Ethylhexyl alcohol (EHA) and tri-n-butyl phosphate (TBP) were used as extractants to separate acetic acid, nitric acid and hydrofluoric acid from the waste etching solution. EHA selectively extracts acetic acid from the waste etching solution, while TBP selectively extracts nitric and hydrofluoric acid. With these extractants, 2 mol/dm(3) of acetic acid was recovered by a 3-stage countercurrent extraction, 10-stage scrubbing and 4-stage stripping; 6 mol/dm(3) of nitric acid was recovered by a 3-stage countercurrent extraction, 10-stage scrubbing and 5-stage stripping; and 6 mol/dm(3) of hydrofluoric acid was recovered by a countercurrent 4 stage extraction and 9-stage stripping. From the results of this study, an acid recovery process for the waste ecthing solution in silicon wafer manufacturing industry was established.