We　describe　a　biosensor　for　phenolic　compounds　that　is　based　on　a　glassy　carbon　electrode　modified　with　tyrosinase　immobilized　on　multiwalled　carbon　nanotubes　(MWNTs).　The　MWNTs　possess　excellent　inherent　electrical　conductivity　which　enhances　the　electron　transfer　rate　and　results　in　good　electrochemical　catalytic　activity　towards　the　reduction　of　benzoquinone　produced　by　enzymatic　reaction.　The　biosensor　was　characterized　by　cyclic　voltammetry,　and　the　experimental　conditions　were　optimized.　The　cathodic　current　is　linearly　related　to　the　concentration　of　the　phenols　between　0.4　mu　M　and　10　mu　M,　and　the　detection　limit　is　0.2　mu　M.　The　method　was　applied　to　the　determination　of　phenol　in　water　samples.