Accurate　condition　assessment　of　power　transformer　is　needed　to　guarantee　transformer　operation　safely　and　reliably.　In　this　paper　the　technique　and　application　of　return　voltage　measurement　and　some　results　of　dielectric　response　measurements　of　several　transformers　was　introduced.　Voltage　response　measurements　were　performed　on　various　transformers　with　different　voltage　grades,　various　operating　periods,　different　moisture　contents　and　aging　degrees　on　site.　Derived　moisture　contents　from　return　voltage　measurement　were　compared　with　the　corresponding　moisture　contents　obtained　from　the　analysis　of　oil　samples.　Based　on　on-site　experiments　and　theoretical　analysis,　the　criteria　for　insulation　state　of　transformer　are　proposed.　Moisture　condition　of　transformer　insulation　can　be　determined　by　using　return　dominant　time　constant,　and　a　good　correlation　between　aging　degree　and　the　return　voltage　initial　slopes　of　the　aged　transformers.　Field　test　performed　on　several　transformers,　its　interpretation　of　results　are　also　presented,　which　proves　that　RVM　measurements　can　be　used　as　a　reliable　tool　for　evaluating　moisture　content　in　transformer　insulation.