Using La0.5Sr0.5CoO3(LSCO) or Pt film as a bottom electrode layer, epitaxial Bi4Ti3O12(BTO) thin films were deposited on MgO(001) substrates by pulsed laser deposition. X-ray diffraction patterns showed that the c-axes of BTO films are oriented normal to the substrate surface. Interestingly, an epitaxial Pt/BTO/Pt film showed a strongly preferred polarization state directed towards the top electrode in spite of the symmetric electrode configuration. The imprint state did not change significantly in the pulse test with DC bias. These anomalous behaviors suggest that the imprint characteristic is highly correlated with interfacial states between the electrodes and the BTO films. To understand space charge effects in the metal-ferroelectric contacts, imprint characteristics of the thin film capacitors with various top electrodes were investigated. Auger Electron Spectroscopy(AES) depth profile was measured, to check the possibility of a interdiffusion of the bottom electrode with the BTO layer. Interdiffusion (or reaction) between the BTO and Pt (bottom electrode) seems to be responsible for the strongly preferred polarization.