Purpose <p>Silicon (Si) plays a crucial role in rice cultivation by inhibiting arsenic (As) uptake and affecting the formation of iron plaque on the root surface (RSIP) of rice. The competitive absorption mechanism between Si and As by rice is relatively well-understood. However, the relationship between the components of the RSIP, its As immobilization capacity, and soil available Si remains unclear.</p> Methods <p>A pot experiment was conducted to investigate the residual effects of exogenous silicon (Si) application on arsenic (As) uptake by rice and the associated changes in chemical and microbiological properties of the rice rhizosphere. During the initial Si application phase (2019–2020), four Si treatment levels were established: 0 (Si0), 50 (Si50), 100 (Si100), and 150 (Si150) mg SiO₂ kg⁻¹ soil. In the subsequent residual effect study period (2021–2023), only base fertilizers including urea, (NH₄) ₂HPO₄, and KCl were applied. After the rice harvest in October 2023, the contents of arsenic and silicon in rice plants, root surface iron plaques, and soil, as well as the microbial diversity of the rhizosphere soil, were determined.</p> Results <p>There was a significant positive correlation between soil available Si content and iron (Fe) content in the RSIP (<i>P</i> &lt; 0.05). The Si enhanced the proportion of ferrihydrite and lepidocrocite fractions in the RSIP and improved their As fixation ability, resulting in less As absorbed by rice. At the optimal silicon application rate of 100&#xa0;mg SiO₂ kg^− 1 soil, the diversity of rhizosphere soil bacteria increased significantly, as did the relative abundance of <i>Sideroxydans</i>, <i>Geobacter</i>, <i>Thiobacillus</i>, and <i>Anaeromyxobacter</i>.</p> Conclusion <p>The Si had a regulatory effect on the microbial community in the rice rhizosphere, such that the formation of the RSIP and its ability to fix As were enhanced, and As content in rice was reduced.</p>