[en] Examination of rubber modified epoxy, cured with diethanol amine, via the transmission electron microscope has shown that a broad distribution of rubber particle sizes exists. The average particle size for particles greater than .1 μm was found to be .8 μm. A significant population of particles was found whose diameters are less than .1 μm. Examination of the particle interface showed that the interface between the dispersed phase and the epoxy matrix was sharp within the accuracy of the method used. The morphology observed was compared against morphologies which have been purported to result in toughening via shear banding and crazing. It was found that the observed particle size distribution did not preclude toughening by these mechanisms