【Objective】The ubiquitous colloidal substances in the environment profoundly affect the transport and transformation of pollutants in soil and groundwater. The impact of microplastics, as an emerging pollutant, on the transport of colloids and colloid-associated pollutants is still unclear.【Method】Therefore, column experiments were conducted in saturated quartz sand, with polystyrene (PS) microplastics as the research object. By combining with sedimentation experiments, Fourier infrared spectroscopy (FTIR), and other methods, the influencing mechanisms of microplastics on soil colloid, copper (Cu2+), and their co-transport were investigated.【Result】The results showed that PS facilitated the transport of soil colloids through mechanisms involving heterogeneous aggregation with soil colloids, competition for surface sites on quartz sand, and steric hindrance. This promotional effect was more pronounced in the presence of Cu2+. In comparison to soil colloid, the effect of PS on Cu2+ migration was not obvious due to its low concentration as well as low adsorption capacity. In the presence of PS, 83.47% of Cu2+ was transported in dissolved form, while 35.25% of Cu2+ was transported in colloidal form under the effluence of soil colloid. PS enhanced the mobility of soil colloids, but it concurrently reduced the adsorption of Cu2+ and facilitated the transport of dissolved Cu2+ compared to the scenario with only soil colloids. However, PS did not have a significant impact on the effluent concentration of total Cu. Furthermore, the mobility of PS was also influenced by soil colloids and Cu2+.【Conclusion】In general, microplastics in the soil environment not only directly interact with Cu2+, but also alter the properties of soil colloids. Changes in colloidal properties may be the primary reason for the impact of microplastics on the environmental behavior of Cu.