A novel micron-sized microencapsulated curing accelerator, imidazole (Im), particles, was first prepared by an ultrasound-assisted dispersing and spray-drying method and can significantly prolong the shelf life of epoxy resin-based microelectronic packaging material. The shell of the encapsulated particles was made from ladderlike copoly(phenyloctyl silsesquioxane) (Ph-Oct-T), which was synthesized by a ''stepwise coupling polymerization'' method. Its softening or flowing temperature can be adjusted by changing the composition. Carbon tetrachloride (CCl4) was chosen as both a solvent of the capsular material Ph-Oct-T and a suspending/precipitating agent of the fine Im particles. Subsequently, the solution containing Ph-Oct-T and suspended Im particles was treated by a spray-drying process to produce the micro encapsulated curing accelerator, Im particles, whose size and appearance was observed by scanning electronic microscopy (SEM). A greatly improved shelf life of the epoxy resin composition containing this microencapsulated curing accelerator was exhibited by curing tests and DSC measurements.