Barium　titanate　[BaTiO3　(BT)]-based　ceramics　are　typical　ferroelectric　materials.　Here,　the　discontinuous　grain　growth　(DGG)　and　relevant　grain　size　effect　are　deeply　studied.　An　obvious　DGG　phenomenon　is　observed　in　a　paradigmatic　Zr4+-doped　BT-based　ceramic,　with　grains　growing　from　∼2.2–6.6　to　∼121.8–198.4　μm　discontinuously　near　1320　.　It　is　found　that　fine　grains　can　get　together　and　grow　into　large　ones　with　liquid　phase　surrounding　them　above　eutectic　temperature.　Then　the　grain　boundary　density　(Dg)　is　quantitatively　studied　and　shows　a　first-order　reciprocal　relationship　with　grain　size,　and　the　grain　size　effect　is　dependent　on　Dg.　Fine　grains　lead　to　high　Dg,　and　then　cause　fine　domains　and　pseudocubic-like　phase　structure　because　of　the　interrupted　long-range　ferroelectric　orders　by　grain　boundary.　High　Dg　also　causes　the　diffusion　phase　transition　and　low　Curie　dielectric　peak　due　to　the　distribution　of　phase　transition　temperature　induced　by　internal　stress.　Local　domain　switching　experiments　reveal　that　the　polarization　orientation　is　more　difficult　near　the　grain　boundary,　implying　that　the　grain　boundary　inhibition　dominates　the　process　of　polarization　orientation　in　fine-grain　ceramics,　which　leads　to　low　polarization　but　a　high　coercive　field.　However,　large-grain　ceramics　exhibit　easy　domain　switching　and　high　&　similar　ferroelectricity.　This　work　reveals　that　the　grain　boundary　effect　dominates　the　grain　size　effect　in　fine-grain　ceramics,　and　expands　current　knowledge　on　DGG　and　grain　size　effect　in　polycrystalline　materials.　©　2023