The crystal structures and characterizations of Ba4EuM3O12 (M = Ru and Ir) are reported. They crystallize in a monoclinic 12-L-perovskite-type structure with space group C2/m. The M3O12 trimers and EuO6 octahedra are alternately linked by corner-sharing and form the perovskite-type structure with 12 layers. The Eu-151 Mossbauer and X-ray photoelectron spectra reveal that the Eu and M ions are in the trivalent and mixed valence (+4.33) oxidation states, respectively. Their electrical conductivities show semiconducting behavior with an activation energy of similar to 0.2 eV above room temperature and demonstrate two-dimensional Mott variable range hopping behavior at low temperatures. The magnetic susceptibility and specific heat measurements indicate that an antiferromagnetic ordering occurs at 4 K, which is due to the magnetic interaction between Ru3O12 trimers. On the other hand, the Ir3O12 trimer is found to be nonmagnetic.