W18O49 nanowire networks have been fabricated by a facile hydrothermal method. In this method, p-aminobenzoic acid (PABA) was used as an assistant agent to control the morphology transformation. W18O49 and its products annealed at different temperature were characterized by XRD, SEM, TEM, UV-vis absorption spectroscopy, XPS, TGA, and FTIR. Formation mechanism and thermal stability of W18O49 nanowire networks were studied in detail. The experiment data showed that PABA played an important role in the induced crystal growth of W18O49 nanowires along [0 1 0] axis. In transformation, the structure of samples was controlled: from irregular particles to nanowire networks. W18O49 nanowire networks were annealed at different temperature. The nanowire networks collapsed at 450 degrees C, while WO3 nanocrystals were obtained. The W18O49 nanowire networks annealed at 400 degrees C have a superior photocatalytic performance to degrade methylene blue and its specific surface area was up to 147 m(2) g(-1). (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.