Polyurea microcapsules containing a pyrethroid insecticide were prepared by the reaction between hexamethylene diisocyanate isocyanurate and ethylenediamine in an oil-in-water emulsion. This study was performed to establish the operational conditions of preparing microcapsules by interfacial polymerization and to investigate how the operational conditions affected the characteristics of microcapsules such as the morphology, wall thickness, mean diameter, and particle size distribution. Microcapsules prepared in this study were found to be spherical and monocore. The microcapsule yields, ranging from 94 to 98%, were almost equal to the theoretical values. The wall thickness of the microcapsules increased with the diameter of the microcapsules and the concentration of hexamethylene diisocyanate isocyanurate. In comparison with the results for microcapsules prepared with a mixture of hexamethylene diisocyanate uretidione and isocyanurate, the diameters and wall thickness of the microcapsules were found to be larger. (c) 2007 Wiley Periodicals, Inc.