This study aimed to develop sustained-release microspheres that can be dispersed on agricultural land using conventional sprayers and thus reduce labor required for pesticide application. Acetamiprid-loaded microspheres of less than 100 mu m in diameter were first prepared through suspension polymerization of pentaerythritol tetraacrylate (PETEA), but were found to release more than 90% of the loaded pesticide within 3 h in water. However, addition of hydrophobic polystyrene to the microspheres decreased the release rate without increasing the microsphere diameter. These results demonstrate that the acetamiprid-loaded polyPETEA/polystyrene microspheres are promising for further reduction of labor due to the controlled release of acetamiprid.