In　this　work,　the　evolution　behavior　of　electrocaloric　effect　in　BaTiO3-based　ceramics　with　different　phase　structures　and　phase　transitions　was　compared.　A　paradigmatic　system　of　(Ba0.85Ca0.15)(Ti1−xHfx)O3　ceramics　was　selected.　Diffuseness　exponent　γ　increases　linearly　with　rising　x.　Electrocaloric　temperature　change　(ΔT)　shows　an　opposite　variation,　whereas　temperature　span　(Tspan)　displays　the　same　tendency　with　γ　changing.　The　degeneration　of　maximum　polarization　and　polarization　change　rate　contributes　to　the　decrease　in　ΔT　due　to　the　diffusion　phase　transition,　whereas　the　diffusion　can　lead　to　a　large　Tspan.　The　ceramic　with　a　single　ferroelectric　or　paraelectric　phase　shows　a　small　ΔT　but　a　high　variation　rate　with　elevating　electric　field　(E),　whereas　a　small　variation　rate　is　present　in　the　phase-transition　region　that　shows　a　high　ΔT.　Besides,　small　electrocaloric　strength　(ΔT/ΔE)　is　obtained　in　the　single-phase　region　and　increases　with　elevating　E.　A　high　ΔT/ΔE　is　present　in　the　phase-transition　region　but　decreases　with　elevating　E.　When　phase　transition　becomes　diffusion,　ΔT　variation　with　E　becomes　obvious,　whereas　ΔT/ΔE　dependence　will　decrease.　These　phenomena　result　from　the　difficult　polarization　orientation　in　single　ferroelectric　phase　or　weak　polarization　in　paraelectric　phase,　and　the　easy　polarization　orientation　in　the　phase-transition　region.　©　2023　The　American　Ceramic　Society.