R. Folkersma et al. had reported that the perikinetic coagulation rate of 2 μm polystyrene(PS) spheres increased remarkably under microgravity conditions. Otherwise, Z. W. Sun et al. had provided their evidence showing that it was only appreciably faster under microgravity than under normal gravity. In order to test the influence of sedimentation on different size of PS spheres, on the basis of Sun's experiments, we have studied the coagulation rates of 1 μm, 2 μm, 3 μm and the mixture of 1 μm and 2 μm PS spheres. Turbidity versus time was employed to monitor the salt-induced coagulation process of PS dispersions. 0.5 mol.L^-^1 MgCl~2 was used to induce fast aggregation. The results show that there is no difference in perikinetic coagulation rate under normal gravity and microgravity for 1 μm, 2 μm, 3 μm and 1 μm+2 μm PS. The authors assumed the surface properties of PS spheres and experimental method might account for the different results.

Key words: SETTLING, MICROGRAVITY, ACCUMULATE, POLYSTYRENE, LATEX