Green roofs are often considered barriers against polluted precipitation, but their effectiveness in capturing airborne microplastics remains unclear. Here we evaluate modular green roofs under simulated wet deposition to assess their ability to intercept and retain microplastics. We find that green roofs remove over 97.5% of deposited microplastics. In Shanghai, China, this corresponds to an annual interception of approximately 1.70 × 10¹² particles, or 56.2 tonnes. Higher rainfall intensity slightly improves capture efficiency by increasing moisture and reducing infiltration forces. Fragment-shaped microplastics are more easily retained than fiber-shaped ones. Most particles are trapped in the soil layer, while some are retained by vegetation, although air turbulence may remobilize fibers. Surface and chemical analysis reveals that plastic materials within green roofs themselves can degrade, potentially releasing microplastics in the process. These results show that green roofs can play a valuable role in reducing urban microplastic pollution and offer practical insights for designing future stormwater and air-quality management strategies.