The ultimate purpose of our research is to demonstrate experimentally the relationship of the deformation and aggregation of red blood cells to the viscosity of blood. We need to measure simultaneously the viscosity of blood and the aggregation of red blood cells. Therefore, we propose a new method to measure simultaneously the viscosity of fluid and the aggregation of particles. The method is developed by combining a cone-plate viscometer with the technique of the particle sizing based on the dynamic light scattering. We show theoretically that a temporal autocorrelation function on the intensity basis is a square of a sum of the autocorrelation functions on the amplitude basis of light scattered from particles and the dynamic speckle produced from the rough surface of a rotating cone in the viscometer. The theoretical prediction is confirmed by experiments for using the solutions of polystyrene latex particles.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.