The spin transport in ferrocene molecules has been examined by using the nonequilibrium Green's function formalism with density functional theory. The ferrocene molecules were sandwiched between the two nickel electrodes in a parallel magnetic configuration, which enhanced the current in comparison with that in an antiparallel spin state and resulting in tunnel magnetoresistance (TMR). The current, having an opposite spin state to that of the ferromagnetic electrode, was the main channel for electron transport. In addition, it became clear that ferrocenylene molecules, having a fulvalene structure with an extended pi-conjugation, enhanced the TMR effect. (C) 2017 Elsevier B.V. All rights reserved.