The hydrothermal crystallization of hierarchical Bi₂WO₆ nanostructures has been monitored with in situ energy-dispersive X-ray diffraction (EDXRD). The kinetic data analysis according to the Avrami-Erofe'ev model suggests that the formation of nanostructured Bi₂WO₆ is diffusion controlled with Avrami exponents around 0.5 and that the growth mechanism is temperature independent in the interval from 150 to 180 °C. Furthermore, the reaction kinetics and the crystal structure of the resulting hydrothermal products depend on the pH value of the Bi(NO₃)₃·5H₂O/K₂WO₄ hydrothermal system.