Microwave　ablation　therapy　using　a　water-cooled　antenna　was　studied　experimentally　in　a　phantom.　The　development　of　the　heating　pattern　induced　by　the　microwave　antenna　was　determined　from　the　thermocouple-measured　temperature　field,　and　the　influence　of　the　cooling　water　flow　within　the　antenna　on　temperature　distribution　and　heating　pattern　was　investigated.　The　shape　of　the　heating　pattern　was　pear-like,　and　the　enlarging　rate　of　the　heating　pattern　decreased　with　heating　time.　Because　of　strong　cooling　effect,　the　heating　pattern　in　the　region　with　Z　＜　0　(where　Z　=　0　represents　the　position　of　radiator,　Z　＜　0　and　Z　＞　0　represent　the　backward　direction　of　the　antenna　with　cooling　water　and　forward　direction　without　water,　respectively)　was　smaller　in　diameter　than　that　with　Z　＞　0,　and　the　heating　pattern　with　Z　＜　0　was　slightly　reduced　when　the　velocity　of　the　cooling　water　increased.　The　highest　ablative　temperature　occurred　with　Z　＞　0　decreasing.　Finally,　the　specific　absorption　rate　distribution　was　also　determined　and　investigated　analytically.　The　present　results　can　be　helpful　in　clinical　ablation　therapy　practice　and　will　be　applicable　to　multiple　applicators　for　surgical　planning.