An aluminoborate, Na_2.5Rb[Al{B₅O₁₀}{B₃O₅}]·0.5NO₃·H₂O (1), was synthesized under hydrothermal condition, which was built by mixed oxoboron clusters and AlO₄ tetrahedra. In the structure, the [B₅O₁₀]^5- and [B₃O₇]^5- clusters are alternately connected to form 1D [B₈O₁₅]_n^6n- chains, which are further linked by AlO₄ units to form a 2D monolayer with 7-membered ring and 10-membered ring windows. Two adjacent monolayers with opposite orientations further form a porous-layered structure with six channels through B—O—Al bonds. Compound 1 was characterized by single crystal X-ray diffraction, powder X-ray diffraction (PXRD), IR spectroscopy, UV-Vis diffuse reflection spectroscopy, and thermogravimetric analysis (TGA), respectively. UV-Vis diffuse reflectance analysis indicates that compound 1 shows a wide transparency range with a short cutoff edge of 201 nm, suggesting it may have potential application in UV regions.