Ester　liquids　are　environmentally　friendly　insulating　oils,　and　they　can　be　used　as　an　alternative　to　mineral　oil　in　transformers,　even　though　in　most　countries　spills　of　ester　oils　must　be　treated　like　spills　of　mineral　oil.　Furthermore,　the　breakdown　characteristics　of　ester　liquids　are　worse　than　those　of　mineral　oils　in　heterogeneous　electric　fields.　In　this　paper,　we　present　a　comprehensive　experimental　research　on　both　positive　and　negative　lightning　impulse　breakdown　properties　in　point-plane　geometries　with　gaps　varying　from　1　mm　to　50　mm.　The　breakdown　voltages　and　streamer　velocities　of　five　kinds　of　ester　liquids,　including　natural　ester,　synthetic　ester,　and　three　kinds　of　single　component　esters　have　been　measured.　The　results　show　that　the　double　bonds　have　no　effect　on　the　breakdown　voltage　of　ester　liquids.　The　average　streamer　velocities　of　mono-esters　are　faster　than　that　of　other　esters　under　positive　polarity,　and　the　breakdown　voltages　of　all　esters　are　close.