Four novel intennetallic silicides, RE5Mn4Al23-xSix (x = 7.9(9),,RE Ho,Er, Yb) and Er44Mn55(AlSi237, have been prepared by reaction in aluminum flux. Three.RE5Mn4Al23,Six compounds crystallize in the tetragonal space group P4/nniirtr with the relatively rare.ddsMgsFe(4)Al(18-x)Si(x) structure type Refinement of single crystal X-ray diffraction data yielded unit : cell parameters of a = 11.3834(9)-114171(10) A and c = 4.0297(2)-4.0575(4) A with volumes ranging from 522.41(5) to. 528.90(8) A3. Structure refinements on single crystal diffraction data show that Er(44)Mri(55)(AlS0237 adopts a new cubic structure . type in the space group Pm3n with a very large unit cell edge of a =21.815(3) A. This new structure is best understood when viewed as two sets of nested polyhedra centered on a main group atom and a manganese atom. These polyhedral clusters describe the majority of the atomic positions in the structure and form a perovskite-type network. We also report the electrical. and magnetic properties of the title compounds. All compounds except the Ho analogue behave as normal paramagnetic metals. without any observed magnetic transitions above 5 K and exhibit antiferromagnetic correlations deduced from the value of their Curie constants. Ho5Mn4Al23_xSix exhibit's a ferromagnetic transition at 20 K and an additional metamagnetic transition at 10K, " suggesting independent ordering temperatures for two distinct magnetic sublattices.