Polyurea microcapsules containing a pyrethroid insecticide were prepared by the reaction between hexamethylene diisocyanate (HMDI) uretidione/isocyanurate and ethylene diamine (ED) in an oil-in-water (O/W) emulsion. This study was performed to investigate how the concentrations of dimer and trimer affect the characteristics of microcapsules such as the morphology, the wall thickness, the size distribution of microcapsules, the microcapsule yield and mechanical property and to investigate the dust mite repellent effect of the microcapsules adhered to the fabrics. Microcapsules prepared in this study were 0.2-6.0 mu m in size and single cored. All the microcapsule yields were almost 98%. It was found that the wall thickness of microcapsules decreases with an increase in the diameter of microcapsudes and increases with an increase in the concentration of HMDI uretidione/isocyanurate. The mechanical property was increased with the concentration of HMDI uretidione/isocyanurate. Polyurea microcapsules showed a high dust mites repellent effect.