  We derive effective Hubbard-type Hamiltonians of $\kappa$-(ET)$_2X$, using an
{\em ab initio} downfolding technique, for the first time for organic
conductors. They contain dispersions of the highest occupied Wannier-type
molecular orbitals with the nearest neighbor transfer $t$$\sim$0.067 eV for a
metal $X$=Cu(NCS)$_2$ and 0.055 eV for a Mott insulator $X$=Cu$_2$(CN)$_3$, as
well as screened Coulomb interactions. It shows unexpected differences from the
conventional extended H\"uckel results, especially much stronger onsite
interaction $U$$\sim$0.8 eV ($U/t$$\sim$12-15) than the H\"uckel estimates
($U/t$$\sim$7-8) as well as an appreciable longer-ranged interaction.
Reexamination on physics of this family of materials is required from this
realistic basis.
