  Possible superconductivity in recently discovered (Tl,K)Fe$_x$Se$_2$
compounds is studied from the viewpoint of doped Mott insulator. The Mott
insulating phase is examined to be preferred in the parent compound at $x=1.5$
due to the presence of Fe vacancies. Partial filling of vacancies at the
Fe-sites introduces electron carriers and leads to electron doped
superconductivity. By using a two-orbital Hubbard model in the strong coupling
limit, we find that the s-wave pairing is more favorable at small Hund's
coupling, and d$_{x^2-y^2}$ wave pairing is more favorable at large Hund's
coupling.
