Metallocenes can be encapsulated inside the carbon nanotubes. The structural, energetic and electronic properties of organometallic MCp 2 @SWCNT are obtained from DFT method. We verify that such encapsulation is noncovalent functionalization, and examined binding energies and charge transfers of MCp 2 @(16,0)SWCNT systems. Consistent with recent experimental findings, the optimal distance between FeCp 2 center and near tube-wall is 4.7 (5.1)Å for the configuration where MCp 2 ’s fivefold axis is parallel (vertical) to nanotube axis, while the minimal diameter is 9.4 (10.2)Å to exothermically encapsulate FeCp 2 molecules. Finally we clarify the doping effects near the band gap by encapsulations of CoCp 2 and NiCp 2 .