The　catalytic　characteristics　of　horse　liver　alcohol　dehydrogenase　(HLADH)　in　the　systems　involving　ionic　liquids　(ILs)　(BMIm•Cl,　BMIm•Br,　BMIm•PF6,　BMIm•BF4　BMIm•OTf　and　EMIm•Cl)　were　examined.　HLADH　displayed　higher　oxidation　activity　towards　ethanol　in　the　systems　containing　BMIm•Cl,　BMIm•Br,　EMIm•Cl　or　BMIm•PF6　with　proper　content　than　that　in　the　IL-free　buffer.　An　excessive　amount　of　these　ILs　in　the　reaction　systems　resulted　in　an　obvious　decline　in　enzymatic　activity.　BMIm•BF4　and　BMIm•OTf　of　any　content　investigated　could　considerably　inhibit　the　enzyme.　The　anions　of　ILs　showed　significant　effect　on　the　activity,　kinetic　parameters　and　activation　energy　of　HLADH-mediated　ethanol　oxidation.　Additionally,　BMIm•Cl,　BMIm•Br,　EMIm•Cl　and　BMIm•PF6　boosted　markedly　the　thermostability　of　HLADH,　while　the　enzyme　was　less　thermostable　in　BMIm•BF4　or　BMIm•OTf-containing　systems.　The　associated　conformational　changes　in　HLADH　caused　by　ILs　were　examined　by　UV　technique.　©　2006　SIOC,　CAS,　&　Wiley-VCH　Verlag　GmbH　&　Co.　KGaA.