【Objective】Microplastics (MPs) and neonicotinoid pesticides are widespread pollutants in agricultural soils, however, their interactions have not been fully studied. Thus, this study aims to explore the interactive mechanisms between biodegradable MPs [poly(butylene succinate), PBS] and neonicotinoid pesticide (thiacloprid, THI). 【Method】The interactive and adsorption mechanisms of THI on PBS were investigated through adsorption kinetics and isotherm models by considering the influence of common environmental factors like pH, salinity, and dissolved organic matter. Also, the desorption of pre-adsorbed THI from PBS using pure water and simulated intestinal fluid (SIF) as background solutions was evaluated. In addition, the bioavailability of THI in red and black soils treated with different proportions of PBS was compared and analyzed using thin film diffusion gradient (DGT) technology. 【Result】The results revealed that the adsorption process of THI on PBS was consistent with the pseudo-second-order kinetic model, indicating that chemical adsorption was predominant. Also, the adsorption isotherm analysis indicated that the adsorption of THI by PBS was multi-layered, and the experimental data fitted both the Henry and the Freundlich models well (R2 > 0.99). The results also showed that an increase in pH and salinity promoted the adsorption of THI while changing the concentration of dissolved organic matter had little effect on the adsorption process. Furthermore, the desorption experiments found that using SIF, the maximum amount of THI desorbed was 39.4 μg?g-1, which was 1.16 times higher than that desorbed by pure water, suggesting that THI is more easily desorbed in the SIF environment. Using the DGT technology, it was observed that the bioavailability of THI in soil increased after the addition of PBS, and the increase became more significant as the ratio of PBS added was increased. 【Conclusion】PBS can adsorb and desorb THI, and when added to soil, PBS can affect the bioavailability of THI. These findings provide important information for understanding the impact of MPs on the environmental behavior of neonicotinoid pesticides under actual environmental conditions and offer a new perspective on the environmental risk assessment and management of pesticides.