Polarization fatigue with repeated electric cycles in ferroelectric thin films is a major degradation problem in ferroelectric nonvolatile memories. However, the origin of this phenomenon is still not properly understood. The fatigue mechanism of a ferroelectric perovskite in a multilayer ferroelectric PbTiO3 thin film material has been investigated here using scanning transmission electron microscopy (STEM). Z-contrast images of the interfaces show that the ferroelectric PbTiO3 layer has partly decomposed into a single crystal PbTiO3 layer and an amorphous layer. Nanometer-sized precipitates are present near the Pt electrode. Electron energy-loss spectroscopy (EELS) analysis reveals that the amorphous layer is a Ti-rich phase between TiO2 and PbTiO3. The precipitates are determined to be a Pt-Pb rich crystalline phase. It is suggested that the formation of the structure-distorted intermediate layer and precipitates may be associated with the ferroelectric degradation process by acting as a passive layer in a ferroelectric capacitor. In addition, the formation of the Pt-Pb rich precipitates may cause an interruption of the consistent Pt electrode, which may result in failure of the device.