Microcapsules containing liquid dicyclopentadiene (DCPD) were synthesized via the in situ polymerization method using urea-formaldehyde (U-F) as a wall material. Variation in the healed fracture toughness was small, with a trend for increased toughness with decreased capsule diameter. The size of microcapsules is very dependent on physical factors, such as the rate of shear and the concentration of stabilizers. Important process parameters, stirring time and speed, emulsifier content, affecting the formation and the morphology of microcapsules, will be investigated.