This paper provides a comprehensive description of the design and commissioning of a dual-stage flow reactor for hydrothermal synthesis, notably heterogeneous nanomaterials such as core−shell particles or nanocomposites. The design is based on the hypothesis that the next frontier of studies within continuous, hydrothermal synthesis lies as much with scalability as it does with the materials properties and performance in applications. Therefore, this reactor belongs to the up-scaled end of a laboratory system with a synthesis capacity of up to 50 g/h. Commissioning was accomplished with TiO 2 nanoparticles as a model material. Results comply with earlier ones obtained from single-stage reactors. Dual-stage synthesis of a TiO 2 @SnO 2 nanocomposite was performed by adding a SnCl 4 solution to newly formed 9 nm TiO 2 nanoparticles, yielding deposition of 2 nm rutile SnO 2 . Synthesis of pure SnO 2 produced much larger nanocrystals, indicating that TiO 2 nanoparticles provide the nucleation sites for SnO 2 and impede the growth beyond 2 nm.