The electrical anisotropy of layer-structured bismuth titanate (Bi4Ti3O12) has been investigated by measurements of Seebeck coefficient, dielectric permittivity, DC conductivity, and complex impedance on single- and polycrystalline samples, and a plausible explanation for the origin of dielectric anomaly below Curie temperature has been suggested. A large anisotropy in the dielectric permittivity, DC conductivity and activation energy for charge transport was observed between the parallel/perpendicular direction to the bismuth oxide layer ((Bi2O2)(2+) layer. Complex impedance and modulus spectroscopy on single crystals in the direction perpendicular to the bismuth oxide layer below the Curie temperature confirmed that there are large differences in the electrical resistivity and, in particular, capacitance between the parallel/perpendicular direction to the bismuth oxide layer, which is assumed to be due to the difference in the electrical nature of the bismuth oxide layer and the pseudo-perovskite block. The dielectric anomaly below the Curie temperature is thought to originate from the space charge due to the thermally agitated polarization fluctuation.