The　electrocaloric　effect　of　ferroelectrics　holds　great　promise　for　solid-state　cooling,　potentially　replacing　traditional　vapor-compression　refrigeration　systems.　However,　achieving　adequate　electrocaloric　cooling　capacity　at　room　temperature　remains　a　formidable　challenge　due　to　the　need　for　a　high　intrinsic　electrocaloric　effect.　While　barium　titanate　ceramic　exhibits　a　pronounced　electrocaloric　effect　near　its　Curie　temperature,　typical　chemical　modifications　to　enhance　electrocaloric　properties　at　room　temperature　often　reduce　this　intrinsic　electrocaloric　effect.　Herein,　a　structural　design　is　introduced　for　barium　titanate-based　ceramics　by　incorporating　isovalent　cations.　This　leads　to　a　well-ordered　local　structure　that　decreases　the　Curie　temperature　to　room　temperature　while　preserving　a　sharp　phase　transition,　enabling　a　large　dielectric　constant　and　tunable　polarization.　This　design　achieves　a　remarkable　electrocaloric　strength　of　~1.0　K·mm/kV,　surpassing　previous　reports.　Atomic-resolution　structural　analyses　reveal　that　the　presence　of　multiscale　nanodomains　(from　~10　nm　to　＞100　nm),　and　the　dipole　polarization　distribution　with　gradual　dipole　rotation　enable　rapid　phase　transition　and　facile　polarization　rotation,　accounting　for　the　giant　electrocaloric　response.　This　work　provides　a　strategy　for　achieving　a　strong　intrinsic　electrocaloric　effect　in　ferroelectrics　near　room　temperature　and　offers　key　insights　into　the　microstructure　landscapes　driving　this　enhanced　electrocaloric　effect.　©　The　Author(s)　2025.