Abstract: The morphology and process of phase-separation of toughening epoxy resin with epoxy-functional poly(n-butyl acrylate) (ETPnBA) and carboxy-functional poly (n-butyl acrylate) (CTPnBA) rubbers were studied by the optical microscope. The effect of curing conditions and prereact time of rubber and epoxy resin on the phase-separation were investigated. The control of the phase-separation and the mechanism of the phase-separation of the modified epoxy resin (by ETPnBA and CTPnBA rubbers) were discussed.