Particles behaviour was monitored and analyzed in a stormwater wetland over a period of 4 months (June-September, 2009). The results indicated that the particles behaviour can be affected by many processes, such as sedimentation, resuspension, adsorption and release in stormwater wetlands during dry days. Due to the effects of these factors, the particles removal efficiency calculated based on the settling theory was significantly higher than the value obtained using the measured particles number con- centration. And the measured efficiency showed a turning point in the range of 2-4 μm, which was within the colloidal particles range. Analysis of particle size distribution showed that particles were finer in the outflow than inflow due to sedimentation of the coarse particles and resuspension of the fine particles in the wet- land. Particles in different size ranges play different roles in their contribution to turbidity and total suspended solids concentration. The finer particles (less than 10μm) showed a closer relationship with the turbidity while coarser particles (〉4μm) were more re- lated to total suspended solid concentration.