The Bi-excess Bi3.25La0.75Ti3O12 (BLT) and Bi3.25La0.75Ti2.91Ta0.09O12 (BLTT) thin films were deposited on Pt (1 1 1)/Ti/SiO2/Si substrates using rf-magnetron sputtering method. The effect of tantalum on mechanical, ferroelectric and dielectric properties of BLT thin films was investigated. XRD patterns reveal that BLT and BLTT thin films have a same second crystalline phase Bi12TiO20, but the former has a randomly oriented major Bi4Ti3O12 phase while the major phase in the later is preferentially oriented along <1 1 7> direction. XPS analysis shows that the substitution of Ta5+ has a significant influence on Ti3+ defects. Mechanical response of thin films is discussed in the light of nano indentation analysis which shows that both the hardness and modulus are reduced with the addition of Ta5+. Ferroelectric properties were improved significantly by Ta5+ doping due to the reduction of Ti3+ defects, and an enhanced remnant polarization (2P(r)) of 32.5 mu C/cm(2) and a decreased coercive field (2E(c)) of 260 kV/cm were obtained. In addition, the Ta substitution elevated the dielectric constant and slightly raised the Curie temperature.