As one of the most promising candidates of high-temperature piezoelectric sensors, BiScO3-PbTiO3 (BS-PT)-based ceramics are commonly modified by end-member substitution to modify the phase structures and electrical properties. In this work, BS-PT-based piezoelectric ceramics with various grain sizes (1.4-3.7 mu m) of the composition 0.98(0.36BiScO(3)-0.64PbTiO(3))-0.02Bi(Sn1/3Nb2/3)O-3 were prepared by conventional solid-state reaction method at different sintering temperatures from 1100celcius to 1180celcius. X-Ray diffraction results show that the tetragonal phase content increases from 68.9% to 85.7% with the increasing sintering temperature. Transmission electron microscope characterizations reveal that micromorphology and domain morphology are sensitive to grain size. In addition, the dielectric and ferroelectric properties are almost independent on the sintering temperature, whereas an optimal piezoelectric constant d(33) of 450 pC/N is achieved when the sintering temperature is 1120celcius, which can be due to the suitable coexistence of the rhombohedral and tetrahedral phase, as well as the coexistence of nanodomains and subsize strip-like domain. All of the results not only open a new window to improve d(33) of piezoelectric ceramics but also help to further understand microstructure-property relationships in piezoelectric ceramics.