The　catalytic　characteristics　of　horse　liver　alcohol　dehydrogenase　(HLADH)　in　a　reaction　medium　containing　ionic　liquid　1-butyl-3-methylimidazolium　chlorate,　[bmim]Cl,　was　examined.　Using　ethanol　as　the　substrate,　the　HLADH　activity　in　the　reaction　system　with　a　[bmim]Cl　content　below　0.　15　g/ml　was　higher　than　that　in　the　medium　without　the　ionic　liquid.　An　excess　amount　of　[bmim]Cl　(＞　0.　15　g/ml)　inhibited　the　enzyme　markedly.　The　effects　of　reaction　temperature　and　pH　on　the　reaction　proceeding　in　the　[　bmim]Cl-containing　system　were　similar　to　those　in　the　[bmim]Cl-free　system.　Compared　with　the　[bmim]Cl-free　system,　the　activation　energy　of　HLADH-mediated　oxidation　of　ethanol　in　the　medium　with　0.05　g/ml　[bmim]Cl　decreased,　and　both　V-max　and　K-m　values　increased.　The　existence　of　[bmim]Cl　at　low　concentrations　(＜=　0.1　g/ml)　in　the　reaction　medium　improved　the　thermal　stability　of　HLADH.　while　the　enzyme　was　more　liable　to　thermally　inactivate　in　the　medium　with　a　[　bmim]　Cl　content　above　0.　1　g/ml.　The　second-derivative　UV　spectroscopy　suggested　that　HLADH　conformations　were　influenced　by　[bmim]Cl.