  We have investigated the electron correlation effect on the electronic
structures and transport properties of the iron-based superconductors using the
density functional theory (DFT) and dynamical mean field theory (DMFT). By
considering the Fe 3d electron correlation using the DMFT, the bandwidth near
the Fermi level is substantially suppressed compared to the conventional DFT
calculation. Because of the different renormalization factors of each 3d
orbital, the DMFT gives considerably reduced electrical anisotropy compared to
the DFT results, which explains the unusually small anisotropic resistivity and
superconducting property observed in the iron-based superconductors. We suggest
that the electron correlation effect should be considered to explain the
anisotropic transport properties of the general d/f valence electron system.
