To prepare cured epoxy resin particles encapsulating a curing agent (diamine), the self-assembly of phase-separated polymer (SaPSeP) method was developed to be applicable to polyaddition reaction of a stoichiometrically imbalanced system. The SaPSeP method was developed by the authors for preparation of micrometer-sized, hollow cross-linked polymer particles by radical polymerization based on the self-assembly of phase-separated polymer at the inner interface of particles. Although a polyaddition reaction, in general, requires that the reactants are in stoichiometric balance for the cure reaction to proceed well, diamine was successfully encapsulated within a cured epoxy resin shell by utilizing the SaPSeP method regardless of stoichiometric imbalance. The results provide further Support of the previously proposed SaPSeP mechanism for the formation of hollow particles. Moreover. Such diamine Capsules can be employed in one-component epoxy adhesives.