In this paper, the properties of a 12-membered-ring open-cage fullerene, which encapsulate La, Ce, Pr, Nd, Pm, Sm, Eu or Gd, as a guest atom, were calculated using first-principle calculations implemented in the DMOL3 package. DFT Semi-core-Pseudo pots spin- unrestricted calculations were carried out with double numerical plus polarization basis set(DNP) and generalized gradient approximation(GGA) of PW91 for the exchange-correlation potential. Calculations show that La etc. Lanthanide metal atoms can be stably adsorbed on the openings of the fullerenes. The average adsorption energy is about-3.647eV in which Pr and Nd have relatively large adsorption energy with -4.748 eV and -4.629 eV, respectively. The Gd is stably adsorbed on the side wall near bottom of the fullerene (see Figure 1 (c)) with adsorption energy of -3.049eV. The PDOS of adsorbed lanthanides were analyzed, respectively. Magnetic property of adsorbed lanthanides was also discussed. From the calculation, it is proved that most of the adsorbed lanthanides keep good magnetic property. Finally, vertical ionization potential and vertical electron affinity of the complex compounds were researched. The results show that the possibility of donating electrons of the 12-membered-ring open-cage fullerene is significantly affected by the endohedral lanthanide metals. From our calculations, it is believed that the complex compounds could be promising candidates for medicine-carrier.