High　depolarization　temperature　(T-d)　and　low　dielectric　loss　(tan　delta)　were　obtained　in　Sc2O3/BiScO3-PbTiO3-Bi(Zn1/2Hf1/2)O-3　(Sc2O3/BS-PT-BZH)　high-temperature　fine-grained　composite　piezoceramics　prepared　by　high-energy　ball　milling　and　one-step　pressureless　sintering.　The　heterogeneous　interfacial　polarization　effect　and　thermal　stress　between　the　Sc2O3　semiconductor　secondary　phase　and　the　BS-PT-BZH　perovskite　piezoelectric　matrix　phase　contribute　to　the　polarization　orientation　of　the　ferroelectric　domain　in　the　electric　field　and　the　maintenance　of　the　poled　ferroelectric　domain　state　under　temperature　excitation,　respectively.　Benefiting　from　the　above　two　heterogeneous　interfacial　effects,　the　Sc2O3/BS-PT-BZH　fine-grained　(similar　to　0.4　mu　m)　ceramic　exhibits　a　high　T-d　of　349　degrees　C,　a　low　tan　delta　of　5.1　%　and　a　moderate　piezoelectric　constant　d(33)　of　495　pC/N,　which　are　comparable　to　those　of　many　BS-PT-based　coarse-grained　(＞2　mu　m)　ceramics.　The　advent　of　Sc2O3/BS-PT-BZH　fine-grained　piezoceramic　is　helpful　to　promote　the　development　of　high-performance　miniaturized　high-temperature　piezoelectric　devices.