Cemented carbide is usually produced by sintering particles of metal carbides with binders. The non-aqueous suspension of both materials is spray-dried to produce granules having uniform material distribution, resulting in the excellent toughness of final products after sintering. Although the status of particle aggregation in a suspension should have a strong relationship with granule properties, the effect of surfactant on aggregative nature of particles has not been systematically investigated. In the present study, a new instrument was developed to measure apparent viscosity of metal particle suspension without sedimentation in order to investigate particle aggregation from the theological point of view. Additionally, the particle interaction has been quantitatively evaluated based on Usui's thixotropy model. It is found that the particle interaction was gradually reduced as increasing surfactant concentration, whereas granule properties changed only at higher concentrations. We also found the suspension stability and product functionality are balanced at the critical concentration. (C) 2014 Elsevier B.V. All rights reserved.