Polycrystalline Bi4Ti3O12 thin films were prepared on fused quartz substrates by pulsed laser deposition. The films were crystallized in the orthorhombic layer perovskite structure confirmed by x-ray diffraction and Raman spectroscopy. The two broad Raman bands centred at 57 and 93cm-1 at 300K break up into clusters of several sharp Raman peaks at 90 K. The temperature dependence of Raman spectra indicates the occurrence of monoclinic distortion of orthorhombic structure at low temperature in the as-prepared Bi4 Tis O12 thin films.