The　effects　of　sintering　temperature　and　soak　time　on　the　sub-grainboundaries　in　ZnO　grains　and　the　effects　of　the　sub-grainboundaries　on　the　electrical　characteristics　of　ZnO　varistor　ceramics　were　investigated.　It　is　found　that　the　sub-grainboundaries　tend　to　disappear　with　the　increasing　of　the　sintering　temperature　and　soak　time.　The　sub-grainboundaries　can　not　only　raise　resistivity　of　ZnO　grains,　but　also　deteriorate　the　pulse　energy　absorption　capability　of　ZnO　varistor　ceramics.