Nanoparticle processing in industry faces major challenges in process scale-up and in maintaining consistency and reproducibility in product quality. Online characterisation of product quality and process conditions can help industry effectively address the challenges, because based on real-time measurements, process control and quality assurance strategies can be developed. This paper investigates the use of dynamic light scattering (DLS), ultrasound spectroscopy (USS) and electrical resistance tomography (EAT) for online characterisation of processes of nanoparticle suspensions. The integrated system provides real-time information of particle size distribution (PSD), zeta potential, conductivity and solid concentration and visualises the mixing behaviour between solid and liquid phases. In addition, ERT provides solid concentration data that is needed by DLS and USS for PSD characterisation. The study focuses on examining the impacts of solid concentration, zeta potential and mixing on the stability of suspension systems and the result of size characterisation. The knowledge learnt provides useful information for applying these sensors to nanoparticle manufacturing processes for online process and product quality control. (C) 2009 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.