Self-healing polymers and composites that incorporate microencapsulated healing agents have demonstrated high levels of healing efficiency in both static and dynamic loading conditions. Microcapsules that contain the healing agent must possess adequate strength, long shelf-life, and excellent bonding to the host material. In previous work we have shown that urea-formaldehyde capules containing dicyclopentadiene (DCPD) prepared by in situ polymerization in an oil-in-water emulsion meet these requirements for self-healing epoxy. However, for standard emulsion encapsulation procedures, a lower limit of size scale is reached ca. 10 μm. Preparation of smaller diameter capsules requires alternative approaches to phase segregation during the encapsulation process. Here we demonstrate an order of magnitude reduction in size scale by a combination of ultrasonication and emulsion polymerization encapsulation techniques. Capsule integrity is demonstrated using scanning electron microscopy and thermogravimetric analysis.