Mn-doped ( Bi0.5Na0.5)(0.94)Ba0.06TiO3 ( MnBNBT) thin films were prepared on SrRuO3 ( SRO)-coated ( 001) SrTiO3 ( STO) single crystal substrates by pulsed laser deposition under different processing conditions. Structural characterization ( i.e., XRD and TEM) confirms the epitaxial growth of STO/SRO/MnBNBT heterostructures. Through the judicious control of deposition temperature, the defect level within the films can be finely tuned. The MnBNBT thin film deposited at the optimized temperature exhibits superior ferroelectric and piezoelectric responses with remanent polarization P-r of 33.0 mu C/cm(2) and piezoelectric coefficient d(33) of 120.0 +/- 20 pm/V.