As an origin of degradation of remnant polarization in Pt/ BaTiO 3 / Pt capacitor structure, an interfacial layer formed at the interface of BaTiO 3 film and a Pt bottom electrode is considered. BaTiO 3 films were deposited on two types of bottom electrodes ͑La 0.5 Sr 0.5 CoO 3 and Pt͒ by the radio frequency magnetron sputtering method and both capacitors showed a microstructural similarity with strong preferred orientations. However, a Pt/ BaTiO 3 /La 0.5 Sr 0.5 CoO 3 capacitor exhibited a saturated hysteresis loop with the remnant polarization ͑2P r ͒ of 6 C/cm 2 , and for the Pt/ BaTiO 3 / Pt structure, the polarization-voltage curve revealed a linear dielectric characteristic. From a cross-sectional high-resolution transmission electron microscope analysis of the Pt/ BaTiO 3 / Pt capacitor showing the linear dielectric property, an interfacial layer with an amorphous structure as well as a multidomain structure in the interior of the BaTiO 3 film were observed. It is concluded that the interfacial layer might help degradation of polarization and its origin can be classified as being extrinsic.