The ternary rare-earth gallium antimonides La13Ga8Sb21 and RE12Ga4Sb23 (RE La-Nd, Sm) have been synthesized through reaction of the elements. The structures of La13Ga8Sb21 (hexagonal, space group D-6h(1)-Pb/mmm, Z = 1, a 17.657(2) Angstrom, c = 4.3378(7) Angstrom) and Pr12Ga4Sb23 (orthorhombic, space group D-2h(25)-Immm, Z = 2, a 4.2612(3) Angstrom, b = 19.4070(13) Angstrom, c = 26.3972(18) Angstrom) have been determined by single-crystal X-ray diffraction. Both structures contain groupings of RE6 trigonal prisms that extend as columns through sharing of the triangular faces. Isolated trigonal planar GaSb3 units result from centering adjacent trigonal prisms by Ga or Sb atoms. Channels outlined by Sb square ribbons linked through Ga-Ga bonding enclose the triangular assemblies of trigonal prisms. The Ga-Ga bonding is manifested as Ga-6-rings in La13Ga8Sb21 but as Ga-2-pairs in Pr12Ga4Sb23. Structural relationships are described between La13Ga8Sb21 and Ba0.8Hf12As17.7, and between Pr12Ga4Sb23 and La6MnSb15.