The discovery of new borates with unique structures has always been a growing part of solid-state chemistry, especially for polyborates. Herein, a new aluminoborate, Cs3AlB6O12, has been discovered by a high-temperature solution in a vacuum system. The highly polymerized [B12O24] cluster, unlike the annular configuration in previously reported polyborates, is found in Cs3AlB6O12 for the first time. The different linkage reflected by the local symmetry in cluster makes these borates not isotypic, although the formula of [B12O24] is identical. Experimental measurement performed on Cs3AlB6O12 powder reveals the deep-ultraviolet transparent spectral feature.