A high piezoelectricity enhancement achieved in (Ba,Ca)(Ti,Sn)O3 lead-free ceramics sintered with 4 mol% Li2O additives by intensifying effect of sintering temperature (TS) in a wide interval (1300–1450 °C) has been found to be related to both the point defects and phase structures. X-ray photoelectron spectroscopy confirmed a reduction of tetravalent cations in B-sites to lower valence state such as Ti3+ and Sn2+ along with an increased content as raising TS. Photoluminescence spectra indicated higher oxygen vacancy concentrations as TS is too low or too high than those at an intermediate TS range, which is attributed to the volatilization of Li+ and the inadequate oxygen supply in environment at high TS. Owing to coexisting rhombohedral and tetragonal phases at room temperature, a high piezoelectric coefficient d33 up to 578 pC/N was achieved as TS=1350 °C.