Heterostructure between layered ferroelectric oxide Bi4Ti3O12 and perovskite (La, Sr)Mn1-x O-3 is highly interesting due to the need to explore new types of functional heterostructures. However, fabricating such heterostructures with high quality is challenging because of the non-isostructural crystalline symmetry of the two constituents. In this work, we constructed two different heterostructures, in which the Bi4Ti3O12 layers with precisely controlled thicknesses were deposited on insulating La0.7Sr0.3Mn0.81O3 and conducting La0.7Sr0.3MnO3 bottom layers, respectively. Results of cross section transmission electron microscopy identified rough interfaces between insulating (La, Sr)Mn1-x O-3 and Bi4Ti3O12, while sharp interfaces between metallic (La, Sr)Mn1-x O-3 and Bi4Ti3O12. In the former, levels of intermixing and charge leaking are strongly dependent on the thickness of the Bi4Ti3O12 capping layer, which induces a capping-layer-thickness-dependent magnetoresistance. These results demonstrated that the interfacial defect is a critical factor for designing functional heterostructures composed of layered oxide and perovskite oxide.