ABSTRACTWe report the growth of sheet-like nanostructured tungsten trioxide hydrate (3WO₃·H₂O) film on fluorine doped tin oxide (FTO) substrate via a facile crystal-seed-assisted hydrothermal method by using CH₃COONH₄ as capping agent. Dense thin film composed of irregular blocks with smaller surface area was obtained without the addition of CH₃COONH_4. X-ray diffraction (XRD) studies indicated that both films were of orthorhombic structure. The nanosheet film grown with CH₃COONH₄ after dehydration showed highly improved photocatalytic activities than the nanoblock one. The maximum anodic photocurrents of 1.16 mA/cm² for oxidization of methanol and 0.5 mA/cm² for water splitting were obtained for the nanosheet film with a highest photoconversion efficiency of about 0.3% under simulated solar illumination.