Hierarchical WO3 nanocakes have been prepared by a green ultrasound-assisted solution chemical route and subsequent heating treatment process. The products have been characterized by XRD, FESEM, TEM, HRTEM, UV–vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra. The results reveal that the as-synthesized cake-like architectures are assembled by multi-layered monoclinic WO3 nanosheets with the thickness of 20–30nm. The band gap energies are estimated to be 2.65eV. PL spectra shows a strong green-light emission band centered around 528nm. A formation mechanism for WO3 nanostructures is simply proposed. More importantly, the cake-like WO3 architectures exhibit the superior photocatalytic activity according to the photodegradation of methylene blue under visible lighting.