Thermal depolarization current (TDC) of a cross‐linked polystyrene composite whose conductive phase is mica has been measured in order to study in detail interfacial polarization (Maxwell‐Wagner effect) in polymer composites with stratified structure. The volume fraction of mica flakes in the composite was varied from 0.16 to 0.37. A peak characteristic of the composites is observed at a temperature above theTgof the composites. The maximum current of the peak increases with the fraction of mica flakes. The behavior of the peak is different from that of TDC due to dipole polarization and the space‐charge polarization of injected electrons. The beginning of a dielectric dispersion corresponding to the peak is observed below 1 Hz at 164 °C. The TDC peak can be explained by Maxwell‐type interfacial polarization. It is proposed that the TDC peak is attributed to interfacial polarization due to trapping or localizing of conductive ions in mica flakes at boundaries between the polymer matrix and mica flakes.