Rubber particle cavitation and concomitant shear deformation of the matrix is known to be a major source of toughening in rubber-modified epoxies. The role of the rubber-matrix interface in this toughening mechanism, however, is not well studied. It has been claimed by Chen and Jan [Polym. Eng. Sci., 31, 577 (1991)] that introduction of a ductile interphase around the rubbery phase enhances plastic dilation of particles and thus contributes to fracture energy of modified blend. In spite of this promising development in rubber toughening, very few studies on the use of ductile interfaces to improve the fracture resistance of rubber-modified polymers have been initiated. The objective of this investigation is to examine the role of ductility of interface on the fracture toughness of rubber-modified epoxies. Both ductile and rigid interphases are incorporated around CTBN particles in a DGEBA epoxy matrix via end-capping of rubber with epoxy monomers different from that of the matrix. The results of this investigation suggest that introduction of a ductile interphase may indeed further improve the crack growth resistance of material under certain test conditions. In contrast, introduction of the rigid interphase, in the system studied, promoted interfacial debonding and plastic dilation but did not alter the mechanical performance of the rubber-modified blend.