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A core-shell type exchange-coupled composite (ECC) structure is developed with an L10 phase FePt core and an Fe shell. Coercivity decreases from 30.6 kOe for the FePt granular film with a very thin thickness of 3.2 nm, to 7.85 kOe for the FePt/Fe core-shell type granular film with a 3-nm-thick Fe. The energy barriers of the FePt/Fe films are measured by using Sharrock equation. A modified formula of gain factor considering the effect of films' thickness is proposed. Core-shell type FePt/Fe ECC granular film has a large advantage over a conventional granular film for media application.