The　phenolic　hydroxyoxime-based　extractant　has　been　discovered　to　degrade　gradually　in　commercial　copper　solvent　extraction　plant.　The　main　degradation　products　occurred　through　hydrolysis　rather　than　oxidation　or　Beckmann　rearrangement,　which　were　identified　as　1-(2-hydroxy-5-nonylphenyl)propan-1-one　and　5-nonyl　salicylaldehyde　through　instrumental　analysis.　The　degradation　products　could　reduce　the　extraction　isotherm,　the　stripping　isotherm　and　the　transfer　of　copper.　Moreover,　the　extractant　regeneration　of　5-nonyl　salicylaldoxime　from　5-nonyl　salicylaldehyde　was　achieved　with　hydroxylamine　sulfate.　It　was　observed　that　the　copper　loading　capacity　of　regenerated　extractant　increased　by　64%,　compared　to　the　copper　loading　of　untreated　hydroxyoxime　extractant.