In this study, the aggregation of particles settling in a shear-thinning fluid is numerically investigated with the distributed-Lagrange-multiplier based fictitious domain (DLM/FD) method. The collocation-element method and a fractional-step scheme based on keeping the Lagrange multiplier at the previous time level in the momentum equations are adopted to discretize the Lagrange multiplier. The lubrication force correction is implemented in the code as a collision strategy. We employ a thixotropic model to account for the time effect of shear-thinning. The results confirm that the memory of shear-thinning is responsible for the aggregation of two end-to-end settling particles, and indicate that the elasticity of the fluid, though may be very weak, seems necessary for the randomly distributed particles to aggregate into stable clusters or columns. (c) 2006 Elsevier B.V. All rights reserved.