The　keto-enol　tautomerization　of　p-hydroxyphenylpyruvic　acid　(pHPP)　in　aqueous　solutions　and　the　complexation　reaction　between　enolic　pHPP　and　boric　acid　have　been　studied　by　electrochemical　techniques　including　linear　sweep　voltammetry　(LSV),　pulse　voltammetry,　and　cyclic　voltammetry　(CV),　combining　with　UV　spectrometry.　Electrochemical　techniques　reveal　that　in　aqueous　solution,　there　are　two　tautomers　of　pHPP:　enolic　form　and　ketonic　form;　the　former　exists　mainly　in　freshly　prepared　pHPP　solution,　and　the　latter　exists　mainly　in　equilibrium　solution.　Both　enolic　and　ketonic　pHPP　are　electroactive.　The　electrochemical　oxidation　of　enolic　pHPP　gives　rise　to　two　anodic　waves,　Ia　and　IIa,　while　the　electrochemical　oxidation　of　ketonic　pHPP　only　results　in　the　observation　of　the　second　wave　IIa.　The　oxidation　process　Ia　is　revealed　to　be　associated　with　the　quasi-reversible,　two-electron　two-proton　oxidation　of　＇C=C＇group　at　the　side　chain　of　enolic　pHPP,　and　the　oxidation　process　IIa　is　proposed　to　result　from　the　irreversible　oxidation　of　phenolic　hydroxyl　group.　It　is　observed　that　in　aqueous　solution,　enolic　pHPP　can　quickly　complex　with　boric　acid　to　yield　enol-borate　complex　that　can　also　oxidize　at　a　glassy　carbon　electrode　to　yield　an　anodic　wave.　©　2003　Elsevier　Science　B.V.　All　rights　reserved.