The effects of annealing temperatures 600, 650, 700, and 750 A degrees C on microstructure, chemical composition, leakage current, ferroelectric, dielectric, and piezoelectric properties of Bi3.15Eu0.85Ti3O12 (BET) thin films prepared by metal-organic decomposition were studied in detail. The largest spontaneous polarization 2P (s) (98.7 mu C/cm(2) under 300 kV/cm), remnant polarization 2P (r) (81.7 mu C/cm(2) under 300 kV/cm), dielectric constant epsilon(r) (889.4 at 100 kHz), effective piezoelectric coefficient d (33) (46.7 pm/V under 260 kV/cm), and lowest leakage current (1.3 x 10(-6) A/cm(2) under 125 kV/cm) of BET thin film were obtained with annealing at 700 A degrees C. The mechanisms concerning the dependence of the enhancement d (33) are discussed according to the phenomenological equation, and the improved piezoelectric performance could make BET thin film a promising candidate for piezoelectric thin film devices.