Novel perpendicularly cross-rectangular CuO architectures have been successfully fabricated on a large scale by a facile microwave-assisted chemical aqueous route. The as-synthesized CuO products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM) and UV-vis absorption spectroscopy. An individual CuO microstructure is mainly assembled by two rectangle-shaped nanosheets with different sizes, which is perpendicularly intersected through the center. A possible formation mechanism of perpendicularly cross-rectangular CuO architectures was proposed based on the comparative experimental results. The prepared CuO nanoarchitectures exhibited excellent photocatalytic activity for the decolorization of Rhodamine B (RhB) under visible light irradiation. Simultaneously, the prepared CuO products, acting as an additive, also showed effective catalytic activity on the thermal decomposition of ammonium perchlorate (NH4ClO4).