Three new oxides Sm2SrCo2O7, Sm2BaCo2O7 and Gd2SrCo2O7 have been synthesized successfully by solid state reaction mathod. The X-Ray diffraction spectra show that they are all isostructural with Sr3Ti2O7, and Ln2SrCo2O7 (Ln=Sm, Gd) crystallized in tetragonal system, Sm2BaCo2O7 in orthrhombic system. The Co-O bonds in CoO2 planes of Ln2SrCo2O7 are shorter than those of LnSrCoO4 (Ln=Sm, Gd), and so their delectrons are more delocalized and their electrical resistivities are smaller. The electrical resistivities versus temperature in the range300-1100K showed that the five oxides show the characters of weakly localized systems. In the lower temperature range, the magnetic behaviors of Gd2SrCo2O7 and GdSrCoO4 fit Curie-Weiss law well, and the magnetic exchange reaction in CoO2 sublattices of Gd2SrCo2O7 is ferromagnetic, but that of GdSrCoO4 is antiferromagnetic. The other three oxides with Sm^3^+ showed complex magnetic behaviors which is perhaps related with the complexity of Sm^3^+.

Key words: COBALT OXIDE, BARIUM OXIDE, STRONTIUM OXIDE, CADMIUM OXIDE, PHASE STRUCTURE, MAGNETIZATION, SAMARIUM OXIDE, ELECTROMAGNETIC PROPERTIES